Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae)

Botanical Journal of the Linnean Society (1996), 120: 89–144. With 19 figures

Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae) MICHAEL WAYNE MORRIS Department of Biology, North Georgia College, Dahlonega, Georgia 30597, U.S.A. AND WILLIAM LOUIS STERN, F.L.S. AND WALTER S. JUDD Department of Botany, University of Florida, Gainesville, Florida 32611-8526, U.S.A. Received August 1995, accepted for publication November 1995

Anatomy of leaf, stem, and root of more than 100 species in subtribe Dendrobiinae (Orchidaceae) was studied with the light microscope to provide a comparative anatomical treatment of these organs, to serve as an independent source of evidence that might be taxonomically important, and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our classification on that of Rudolf Schlechter as the most complete and widely accepted today. We found that the anatomy of plants in subtribe Dendrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these anatomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of Dendrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the difficulty of determining the phylogenetic relationships of many of Schlechter’s sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications based on available data, be retained for the present, pending a more detailed understanding of the phylogeny of Dendrobiinae based on morphology, micromorphology, anatomy, and DNA studies. ©1996 The Linnean Society of London

ADDITIONAL KEY WORDS: — Epigeneium – Dendrobium – Cadetia – Pseuderia – Flickingeria – Eria – Diplocaulobium – Porpax – tilosomes – exodermal V-thickenings.. CONTENTS Introduction . . . . . . . . . Material and methods . . . . . . Results . . . . . . . . . . . Anatomy of Cadetia . . . . . Sections Pterocadetia and Cadetia . Generalized anatomy of Dendrobium Section Desmotrichum . . . . . Section Goniobulbon . . . . . Section Diplocaulobium . . . . Section Bolbidium . . . . . . Section Rhizobium . . . . . .

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©1996 The Linnean Society of London

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M. W. MORRIS ET AL. Section Sarcopodium . . . Section Dendrocoryne . . . Section Latouria . . . . Section Inobulbon . . . . Section Callista . . . . . Section Dendrobium . . . Section Platycaulon . . . . Section Pedilonum . . . . Section Brachyanthe . . . Section Stachyobium . . . Section Phalaenanthe . . . Section Eleutheroglossum . . Section Spatulata . . . . Section Formosae . . . . Section Rhopalanthe . . . Section Aporum . . . . . Section Grastidium . . . . Section Macrocladium . . . Section Monanthos . . . . Sections Phalaenanthe/Spatulata Anatomy of Pseuderia . . . Discussion . . . . . . . . Cladistics . . . . . . . . Conclusions . . . . . . . Acknowledgements . . . . . References . . . . . . . .

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INTRODUCTION

Tribe Dendrobieae Endl. consists of subtribes Bulbophyllinae Schltr. and Dendrobiinae Lindl. (Dressler, 1993). Dendrobiinae are a numerically and taxonomically significant component of Orchidaceae comprising six genera and approximately 1147 species primarily of the Old World tropics and subtropics. The subtribe is not represented in Africa or Madagascar. Species are known from Korea and Japan in the north to India, Sri Lanka, Australia, and New Zealand in the south. Dressler holds Dendrobiinae to be “…one of the most distinctive and natural” groups among Orchidaceae and included the genera Cadetia Gaudich., Dendrobium Sw., Diplocaulobium (Rchb. f.) Kraenzl., Epigeneium Gagnep., Ephemerantha Hunt & Summerh. (Flickingeria A.D. Hawkes), and Pseuderia Schltr. in his concept of the subtribe. Schlechter (1912), on the other hand, included not only Cadetia, Dendrobium (including Diplocaulobium, Epigeneium, and Flickingeria as sections), and Pseuderia, but also Eria Lindl., Cryptochilus Wall., and Porpax Lindl. in Dendrobiinae. We followed Dressler’s more recent treatment in excluding Eria, Cryptochilus, and Porpax from Dendrobiinae, but complied with Schlechter’s more detailed generic, subgeneric, and sectional classification for the remaining taxa in the subtribe (Table 1). Schlechter’s subgeneric and sectional system is the most recent overall treatment and with certain modifications, it is the classification most modern authorities follow (Seidenfaden, 1992; Seidenfaden & Wood, 1992; Phillip J. Cribb, Robert L. Dressler, personal communication). Dendrobiinae comprise primarily epiphytic plants, although some are lithophytic or terrestrial. Features that most readily distinguish Dendrobiinae are associated with floral morphology, because there is wide vegetative morphological diversity in the group. For Dendrobium, Bechtel, Cribb & Launert (1992) wrote, “Flowers… rather more constant morphologically than the vegetative characteristics.” Flowers are small to large and resupinate, very short-lived or very long-lasting. The fused basal

ANATOMY AND SYSTEMATICS OF DENDROBIINAE (ORCHIDACEAE)

TABLE 1. Specimens examined arranged according to Schlechter (1912)a,b Taxa Cadetia Gaudich. Section Pterocadetia Cadetia collina Schltr. C. obliqua Schltr. C. taylori (F. Muell.) Schltr. Section Cadetia C. hispida (A. Rich.) Schltr. C. pomatophila Schltr. Dendrobium Sw. Subgenus Athecebium Section Desmotrichum Dendrobium angustifolium (Blume) Lindl. D. comatum (Blume) Lindl. D. comatum D. macraei Lindl. D. pallens Ridl. D. pallens D. pardalinum Rchb.f. D. plicatile Lindl. D. xantholeucum Rchb.f. Section Goniobulbon D. chrysotropis Schltr. Section Diplocaulobium D. arachnoideum Schltr. D. fariniferum Schltr. D. guttulatum Schltr. Section Bolbidium D. pachyphyllum (R.E. Kunze) Backh.f. Section Rhizobium D. cucumerinum Macleay ex Lindl. D. lichenastrum (F. Muell.) Kraenzl. emend. Dockrill D. linguiforme Sw. D. pugioniforme A. Cunn. D. rigidum R. Br. D. schoeninum Lindl. D. teretifolium R. Br. D. toressae (F.M. Bailey) Dockrill D. wassellii S.T. Blake Section Sarcopodium D. amplum Lindl. D. cymbidioides (Blume) Lindl. D. lyonii Ames Section Dendrocoryne D. jonesii Rendle D. kingianum Bidwill D. macropus (Endl.) Rchb.f. ex Lindl. subsp. gracilicaule (F. Muell.) P.S. Green D. speciosum Sm. D. tetragonum A. Cunn. Section Latouria D. johnsoniae F. Muell. D. macrophyllum A. Rich. D. macrophyllum Section Inobulbon D. munificum (Finet) Schltr. Section Callista D. amethystoglossum Rchb.f. D. chrysotoxum Lindl. D. densiflorum Wall. ex Lindl. D. griffithianum Lindl.

Available materialc Origind

RSL RSL RSL

K 394-82-04251 SEL 81-2242 K 342-84-03518

RSL RSL

K 247-82-02372 SEL 77-2781

RhSL RL RRhL RRhSL RL RhL RSL RL RRhSL

SEL hort. K 394-82-04275 SEL hort. SEL hort. K 102-83-00707 MO hort. MO hort. K 721-63-72101 SEL hort.

RSL

SEL hort.

RRhL R RRhSL

K 351-75-03382 K 587-86-05699 SEL hort.

RSL

MO hort.

RL RRhL RL L RRhL R RL RRhL RL

WLS hort. FLAS WLS hort. FLAS WLS hort. WLS hort. WLS hort. FLAS WLS hort. FLAS WLS hort. WLS hort. WLS hort. FLAS

RL RSL RL

K 439-84-04649 K 705-63-70522 K 705-63-70522

RSL RL

MO hort. WLS hort.

RSL RL RSL

MO hort. WLS hort. FLAS MO hort.

RSL RSL RSL

SEL 74-23-1059 MO hort. AMP hort.

SL

RWR hort.

RL RSL RL RSL

WLS hort. WLS hort. FLAS WLS hort. WLS hort. FLAS

91

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TABLE 1. (continued) Taxa Dendrobium Sw. (continued) Subgenus Athecebium (continued) Section Callista (continued) D. lindleyi Steud. D. palpebrae Lindl. D. thyrsiflorum Rchb.f. Subgenus Dendrobium Section Dendrobium D. albosanguineum Lindl. D. aphyllum (Roxb.) C.E.C. Fisch. D. capillipes Rchb.f. D. chrysanthum Wall. ex Lindl. D. dixanthum Rchb.f. D. falconeri Hook. D. fimbriatum Hook. D. findlayanum Parish & Rchb.f. D. loddigesii Rolfe D. moschatum (Buch.-Ham.) Sw. D. nobile Lindl. D. parishii Rchb.f. D. pendulum Roxb. D. primulinum Lindl. D. pulchellum Roxb. ex Lindl. D. senile Parish ex Rchb.f. D. signatum Rchb.f. D. tortile Lindl. Section Platycaulon D. lamellatum (Blume) Lindl. D. platygastrum Rchb.f. Section Pedilonum D. bracteosum Rchb.f. D. bullenianum Rchb.f. D. secundum (Blume) Lindl. D. smillieae F. Muell. Section Brachyanthe D. alterum Seidenf. D. hercoglossum Rchb.f. Section Stachyobium D. compactum Rolfe D. delacourii Guillaumin Section Phalaenanthe D. bigibbum Lindl. D. williamsianum Rchb.f. Section Eleutheroglossum D. fellowsii F. Muell. Section Spatulata D. antennatum Lindl. D. canaliculatum R. Br. D. taurinum Lindl. Section Formosae D. cruentum Rchb.f. D. dearei Rchb.f. D. formosum Roxb. ex Lindl. D. sanderae Rolfe D. schuetzei Rolfe D. virgineum Rchb.f. Subgenus Rhopalobium Section Rhopalanthe D. clavator Ridl. D. crumenatum Sw.

Available materialc Origind

RSL L RL

MO hort. WLS hort. WLS hort. FLAS

RL RL L RL RSL SR RL RL RSL RL RL RL RL RL RL RL RSL SL

WLS hort. WLS hort. FLAS WLS hort. WLS hort. WLS hort. MO hort. WLS hort. FLAS WLS hort. WLS hort. FLAS WLS hort. WLS hort. FLAS WLS hort. FLAS WLS hort. WLS hort. FLAS WLS hort. FLAS WLS hort. MO hort. MO hort.

RSL RSL

MO hort. SEL 75-89-051

RSL RL RSL RSL

MO hort. WLS hort. FLAS WLS hort. MO hort.

RSL RSL

MO hort. WLS hort.

RSL RSL

MO hort. MO hort.

L RSL

WLS hort. MO hort.

RL

WLS hort. FLAS

RSL RSL RL

MO hort. MO hort. WLS hort.

RL RSL RSL RL RL RL

WLS hort. MO hort. WLS hort. WLS hort. FLAS WLS hort. WLS hort.

RSL RSL

WLS hort. WLS hort.

ANATOMY AND SYSTEMATICS OF DENDROBIINAE (ORCHIDACEAE)

93

parts of the lip and the lateral sepals, and sometimes also the petals, appear as a ventral extension of the column carrying the lip in most species and forming a column-foot (Rasmussen, 1985). We consider these conditions synapomorphic for the subtribe; however, they were presumably lost in Pseuderia. The column-foot and sepals may form a mentum or chin-like projection. The two-celled anther is terminal and incumbent with four (sometimes two) ‘naked pollinia’, that is, well-developed pollinia lacking any appendages or accessory structures. Dendrobiinae thrive in diverse habitats with respect to substrates, moisture regimes, elevations, latitudes, and exposures. It appears that the species, which occur across this broad range of ecological situations, reflect this variability through their vegetative diversity; the various species apparently adapt to certain modes of existence. Most plants have stems of several internodes: these range from globose to clavate (pseudobulbs) to long, slender, and reed-like. Some taxa exhibit highly branching pseudobulb-bearing rhizomes such as those in section Desmotrichum in Dendrobium (Rasmussen, 1982). Relatively few species lack conspicuously thickened stems altogether (e.g. Dendrobium sections Rhizobium and Aporum) and instead possess

TABLE 1. (continued) Available materialc Origind

Taxa Dendrobium Sw. (continued) Subgenus Xerobium Section Aporum D. acerosum Lindl. D. acinaciforme Roxb. D. anceps Sw. D. leonis (Lindl.) Rchb.f. Section Grastidium D. salaccense (Blume) Lindl. D. salaccense Section Macrocladium D. cunninghamii Lindl. Section Monanthos D. malbrownii Dockrill Phalaenanthe/Spatulata D. x superbiens Rchb.f. Pseuderia Schltr. Pseuderia foliosa (Brongn.) Schltr. P. micronesiaca Schltr.

RSL RSL RSL L

MO hort. MO hort. WLS hort. FLAS WLS hort. FLAS

RSL RL

MO hort. WLS hort. FLAS

RSL

A.F. Mark s.n., New Zealand

RSL

SEL hort.

RSL

WLS hort.

SL SL

Kornassi 1147 AMES T. Hosokawa 9259 AMES S. Vodonaivalu s.n. FLAS T.G. Yuncker 9251 AMES P.F. Hunt 2251 AMES S. Vodonaivalu s.n. FLAS

P. platyphylla L.O. Williams

RSL

P. ramosa L.O. Williams

SL

P. similis (Schltr.) Schltr. P. smithiana C. Schweinf.

SL RSL

aOnly those of Schlechter’s taxa represented in our study material are included in this listing. bAbbreviations of authorities for binomials are those recommended by Brummitt & Powell (1992). cR=root; Rh=rhizome; S=stem (pseudobulb); L=leaf. dAMES= Orchid Herbarium of Oakes Ames; FLAS=University of Florida; K=Royal Botanic Gardens,

Kew; MO=Missouri Botanical Garden; SEL=The Marie Selby Botanical Gardens; AMP=hort. Alec M. Pridgeon; RWR=hort. Robert W. Read; WLS=hort. William Louis Stern. Abbreviations of herbaria are according to Holmgren, Holmgren & Barnett (1990).

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elongated, fleshy or slender rhizomes, or have slim, lax to rigid stems of many internodes (e.g. section Grastidium in Dendrobium). Dendrobium is by far the most species-rich (about 900; Bechtel et al., 1992; Mabberley, 1993) of the genera in Dendrobiinae. Leaves in Dendrobiinae are commonly distichous, conduplicate, and articulate, but they range from terete and coriaceous, to laterally flattened, fleshy, and equitant to grass-like. Leaves may be persistent or deciduous. Persistent and succulent leaves commonly store water (Holttum, 1960), whereas in those species that are deciduous, leaves are carried only during the wetter portion of the year. In this case, the bare stem serves as a food- and water-storing organ over the dry season, while at the same time the absence of leaves serves to decrease water loss during this stressful period. Leaves and pseudobulbs of some species have dark trichomes; others have shaggy silvery-gray hairs. Leaf size and plant dimensions among Dendrobiinae also vary widely. Roots in Dendrobiinae are typically slender, moderately fleshy, and velamentous. The ‘extreme’ range of morphology is neatly summed in Bechtel et al. (1992) and is given as a major reason for the inability of botanists to understand the species and “to group like-species within the genus [Dendrobium] into a workable system of sections.” Certain tissues are characterized by stegmata, cells containing spherical silica bodies (Tomlinson, 1961; Møller & Rasmussen, 1984), a ‘Dendrobium type’ velamen (Porembski & Barthlott, 1988), and significant amounts of sesquiterpenoid alkaloids (L¨uning, 1974; Slaytor, 1977). Among anatomical features generally regarded as important in determining systematic relationships in Orchidaceae, for Dendrobiinae we examined the velamen, stomatal configuration, and silica bodies in stegmata, as well as the general configuration of tissues in leaf, stem, and root considering the methods and descriptions employed in anatomical papers of Williams, 1979; Pridgeon, 1982, 1987; Pridgeon, Stern & Benzing, 1983; Møller & Rasmussen, 1984; Rasmussen, 1987; Porembski & Barthlott, 1988; Stern, Morris & Judd (1994), R¨uter & Stern (1994). Only certain species in Dendrobiinae have been studied anatomically, these usually as part of broad investigations of particular features rather than as complete studies of specific taxa. For example, Solereder & Meyer’s (1930) anatomical compendium of Orchidaceae has scattered references to vegetative features of different genera, but there is no systematically based body of information on any one genus. Table 2 is an overview of literature on vegetative anatomical studies involving members of Dendrobiinae. It is beyond the scope of our paper to present a general discussion of the taxonomy of Dendrobiinae. Useful reviews of taxa in the subtribe and some of the sections, genera, and species can be found in Schlechter (1912), Cribb (1983, 1986), and Bechtel et al. (1992). Schelpe & Stewart (1990) list some recent sectional and generic nomenclatural changes. The only comprehensive treatment of Dendrobium was published by Kr¨anzlin in 1910, but it has been deprecated by Schlechter (1912) and others. Although we recognize Dendrobium as a large paraphyletic grouping, others (e.g. Seidenfaden, 1992; Seidenfaden & Wood, 1992) have sought to maintain as genera separate from Dendrobium, Flickingeria A.D. Hawkes ( = Dendrobium sect. Desmotrichum of Schlechter), Epigeneium Gagnep. ( = Dendrobium sect. Sarcopodium of Schlechter), and Diplocaulobium ( = Dendrobium sect. Diplocaulobium of Schlechter). Also, Schlechter’s (1912) section Eugenanthe is referred to here as section Dendrobium, section Oxygenianthe (or Nigrohirsutae by others) as section Formosae, and section Ceratobium as section Spatulata (Bechtel et al., 1992; Cribb, 1986). Dendrobium canaliculatum, placed by

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TABLE 2. Earlier anatomical studies. Authorities included only for those taxa not cited in the text Author

Date

Parts studied

Chatin Chatin Leitgeb

1856 1857 1864

Root Rhizome, pseudobulb, leaf Root

Möbius

1887

Leaf

Pfitzer Meinecke Went Baranetzky Janse Richter Malte

1889 Root 1894 Root 1895 Root 1897 Shoot apical meristem 1897 Root 1901 Root 1902 Root, stem, leaf

Tominski Lancaster Curtis Engard Kraft Yamazumi Dycus & Knudson Kuttelwascher Morisset Takahashi, Namba & Hayashi Chiang Gupta, Ansari & Kapoor

1905

Leaf

Mejstrík Chiang & Chou

1910 Root 1917 Root, stem, leaf 1944 Root 1949 Root 1952 Leaf (abscission) 1957 Root 1964 Root 1964 Root 1965 Root, rhizome, pseudobulb 1970 Root 1970 Root, rhizome, pseudobulb, leaf 1970 Root 1971 Root

Hadley & Williamson

1972

Barthlott & Capesius Subrahmanyam

1975 1976

Williams

1979

Namba & Lin

1981

v

Taxa Dendrobium sp. Dendrobium fimbriatum, D. speciosum Dendrobium speciosum, Sarcopodium lobii (D. lobbii Teijsm. & Binn.) Dendrobium fimbriatum, D. wardianum Warner, D. cambridgeanum Lindl., D. dalhousianum Paxton, D. densiflorum, D. pierardii (D. aphyllum) Dendrobium nobile Dendrobium chrysanthum, D. nobile Dendrobium crumenatum Dendrobium nobile Dendrobium sp. Dendrobium speciosum Dendrobium brymerianum Rchb.f., D. crystallinum Rchb.f., D. findlayanum, D. moschatum, D. thyrsiflorum Dendrobium macarthiae Thwaites, D. aureum Lindl., D. macrostachyum Dendrobium cunninghamii Dendrobium cunninghamii Dendrobium sp. Dendrobium speciosum Dendrobium monile Kraenzl. Dendrobium nobile Dendrobium moschatum Dendrobium nobile Dendrobium lohohense T. Tang & Chen H. Wang, D. nobile, D. plicatile Lindl. Dendrobium kwashotense Hayata Dendrobium macraei

D. cunninghamii Dendrobium fimbriato-labellum Hayata, D. flaviflorum Hayata Root Dendrobium cornutum Hook.f., D. longipes Hook.f., D. crumenatum Root Dendrobium superbum Rchb.f. Root, rhizome, stem, Dendrobium barbatulum Lindl., leaf D. microbulbon A. Rich., D. aqueum, Katherinia (Dendrobium) fuscescens (Griff.) Hawkes Leaf surface Cadetia taylori, Dendrobium bicameratum Lindl., D. crumenatum, D. densiflorum, D. farmeri Paxton, D. fimbriatum, D. findlayanum, D. hercoglossum, D. hildebrandii Rolfe, D. malbrownii, D. palpebrae, D. pierardii (D. aphyllum), D. teretifolium, D. terminale, D. thyrsiflorum a,b Root, rhizome, pseudobulb Dendrobium clavatum (Rchb.f.) T. Tang & Chen H. Wang, D. moniliforme (L.) Sw., Ephemerantha (Dendrobium) comata, Dendrobium furcatopedicellatum Hayata, D. tosaense Makino, D. miyakei Schltr., D. crumenatum, D. somai Hayata, D. equitans Kraenzl., D. chameleon Ames, D. linawianum Rchb.f., D. falconeri, D. leptocladum Hayata, Ephemerantha (Dendrobium) pallens, Dendrobium nakaharaei Schltr., D. sanseiense Hayata

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TABLE 2. (continued) Author

Date

Part studied

Taxa

Singh

1981

Leaf surface

Møller & Rasmussen

1984

Root, rhizome, pseudobulb, leaf

Singh

1986

Root

Porembski & Barthlott

1988

Root

Khasim & Rao

1989

Root, stem, leaf

Rao et al.

1989

Root, stem, leaf

Dendrobium alpestre Royle, D. amoenum Wall., D. candidum Lindl., D. chrysanthum, D. chrysotoxum, D. densiflorum, D. macrostachyum Lindl., D. moschatum, D. nobile, D. pierardii (D. aphyllum), D. peguanum Lindl., D. secundum, D. transparens Wall. Dendrobium falconeri, D. findlayanum, D. heterocarpum Lindl., D. leonis, D. pallens Dendrobium alpestre, D. amoenum, D. chrysotoxum, D. densiflorum, D. pierardii (D. aphyllum) Dendrobium moschatum, D. nobile, Diplocaulobium (Dendrobium) sp., Epigeneium (Dendrobium) sp., Flickingeria (Dendrobium) fimbriata Dendrobium densiflorum, D. nobile, D. moschatum, D. rotundatum Benth. Dendrobium chrysanthum

Schlechter (1912) in section Eleutheroglossum, is properly located in section Spatulata (Cribb, 1986). The well-known and widely cultivated D. aggregatum Roxb. must be called D. lindleyi Steud. owing to an earlier use of the former name by Kunth (Bechtel et al., 1992). We have made other nomenclatural changes in accordance with recent literature, but we have not exhaustively combed all references. Our investigation of Dendrobiinae was undertaken to: (1) provide a comparative anatomical treatment of the vegetative organs; (2) serve as an independent source of evidence that might be taxonomically important; and (3) recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of anatomical data. We were interested in examining the proposed monophyly of the genera and infrageneric taxa recognized by Schlechter, and the organization of Dendrobiinae advocated by Dressler. An assessment of the vegetative anatomy of taxa proposed for inclusion in Dendrobiinae may provide new information for understanding this subtribe of Orchidaceae.

MATERIAL AND METHODS

Vegetative parts of 100 taxa in Dendrobiinae were studied. These parts represented two sections and five species in Cadetia, 24 sections, 88 species, and one natural hybrid in Dendrobium, and six species in Pseuderia (Table 1). Most samples were secured from greenhouse-grown plants, but a few specimens were collected from the field. Material of Pseuderia foliosa, P. micronesiaca, P. ramosa, and P. similis was obtained from herbarium specimens (Table 1). Tissues were prepared for study using standard microtechnical methods for anatomy as described by Cutler (1978) and especially by Metcalfe (1971) for monocots. These techniques involved killing and fixing the tissues in FAA (commercial formalin, glacial acetic acid, and 70% ethanol in the ratio of 0.5:0.5:9.0 parts, respectively) and then storing in 70% ethanol prior to sectioning. Dried stems

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and leaves of the four Pseuderia species mentioned above were boiled in water to hydrate and softened in a 1:3 solution of ‘Aerosol OT’ (Fisher Scientific Company) and deionized water according to Ayensu’s (1967) method. Plant parts were then sectioned on a sliding microtome; mid-regions of stem and leaf blade and the most mature region of the root available were taken. Transverse and longitudinal sections of leaf and root and transverse sections of stem were cut. Tissues were stained in haematoxylin and safranin and mounted in Canada balsam on microscope slides for observation. Some sections were not stained so that crystals and other deposits would not be destroyed or otherwise altered during processing. Scrapings of leaf blades followed Cutler’s (1978) technique and were stained in safranin. Observations were made with the Nikon Optiphot microscope and photomicrographs were taken with Nikon’s HFX-DX system. Lengths and widths of ten guard-cell pairs were measured (Table 3). Stomatal terminology follows Tomlinson (1974) and Wilkinson (1979) as it applies to our material, methods of preparation and examination. Cuticle thickness categories were established as follows: < 3 µm = thin, 3–10 µm = moderately thick, > 10 µm = thick. For epidermal wall thickness we considered < 3 µm = thin, 3–5 µm = somewhat thick-walled, > 5 µm = thick. ‘Cruciate’ starch grains are TABLE 3. Dimensions of guard-cell pairs Range µm Genus Section

Length

Cadetia Pterocadetia Cadetia Dendrobium Desmotrichum Goniobulbon Diplocaulobium Bolbidium Rhizobium Sarcopodium Dendrocoryne Latouria Inobulbon Callista Dendrobium Platycaulon Pedilonum Brachyanthe Stachyobium Phalaenanthe Eleutheroglossum Spatulataa D. canaliculatum (abaxial) D. canaliculatum (adaxial) Formosae Rhopalanthe Aporum Grastidium Macrocladium Monanthos Phalaenanthe/Spatulata Pseuderia aDendrobium

Width

Mean µm Length

× Width

20–33 33–38

15–23 25–33

26 35

20 28

18–35 33–35 30–35 28–30 33–58 23–35 30–50 35–60 40–45 20–41 25–50 23–25 23–40 23–48 30–43 38–45 35–41 35–48 53–60 50–61 28–60 28–45 23–45 20–28 40–45 26–30 38–43 25–38

15–33 33–35 30–35 23–28 28–58 23–28 28–50 30–55 30–38 20–38 18–43 18–25 18–33 23–38 20–25 28–43 34–43 28–45 43–51 48–53 20–48 28–35 20–35 18–24 35–42 24–28 35–40 20–33

25 33 33 28 43 29 39 49 42 31 37 28 29 35 35 43 38 42 56 59 40 35 33 24 43 28 40 32

24 33 32 25 42 25 36 42 35 27 27 21 24 28 22 34 37 38 48 51 33 30 27 21 39 26 38 26

antennatum and D. taurinum; D. canaliculatum is amphistomatal.

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those birefringent granules in which a dark, equal-armed cross appears when viewed under crossed Nicol prisms. We use the term ‘isodiametric’ to refer to cells that are equilateral seen in section. Our use of ‘phloic’ means of, at, or near the phloem, and ‘xyloic’ means of, at, or near the xylem. In describing the outlines of water-storage cells in leaves and stems, we use the terms pleated and unpleated, that is, whether in section cell outlines appear grooved or not. The inner tangential walls and adjacent portions of the anticlinal walls of cells in the innermost layer of the velamen abutting the exodermis are exceptionally thickened in some species of Dendrobium. We have designated these specially thickened walls as V- or <-thickened. Other anatomical terminology is based on that in recently published papers, e.g. Pridgeon (1982, 1987), Pridgeon & Stern (1982), Pridgeon, Stern & Benzing (1983), Stern & Morris (1992), Stern et al. (1993); Stern, Pridgeon & Luer (1985). Detailed measurements and descriptions, from which those appearing in this paper are condensed, appear in Morris (1993). Because of the many anatomical features held in common by members of the sections of Dendrobium, we drew up a generalized description for the genus to account for these similarities. The sectional treatments that follow by and large contain information that differs in some way from the generalized treatment. Cadetia and Pseuderia are each represented by a single statement that applies to the anatomy of the entire genus as exhibited by our material. Schlechter’s 1912 work on the Orchidaceae of German New Guinea and Dressler’s 1993 treatise on the phylogeny and classification of Orchidaceae are cited repeatedly throughout our discussions. To alleviate the redundancy resulting from this, we have omitted the years of publication following the first notice in each case. Because these are the only studies by these two authors reported here, there should be no confusion.

RESULTS

Anatomy of Cadetia Species examined: C. collina, C. hispida, C. obliqua, C. pomatophila, C. taylori. Leaf surface. HAIRS: uniseriate, uni- to bicellular, glandular, sunken, ambifacial; birefringent anastomosing thickening bands in walls of crypt cells around hair bases. EPIDERMIS: cells polygonal, anticlinal walls more or less straight-sided on both surfaces, curvilinear in many cells, the angles then rounded. STOMATA: abaxial, paracytic; ranges of means for guard cell pairs: 25–35 µm long, 18–28 µm wide (Table 3). Leaf (T.S.). Leaves conduplicate. CUTICLE: moderately thick, smooth to irregular. cells elliptical to oval to polygonal; adaxial cells approximately same size as abaxial cells; somewhat thick-walled. STOMATA: superficial, substomatal chambers small, outer ledges rather large, inner ledges minute. HYPODERMIS: 1-layered, adaxial and abaxial, weakly to well-defined, most cells rounded to polygonal, thin-walled, some cells with helical cell wall thickenings (Table 4). FIBRE BUNDLES: absent. CHLORENCHYMA: heterogeneous, assimilatory cells living, thin-walled, forming a network; water-storage cells dead, thin-walled, empty, scattered, mostly larger than assimilatory cells, walls with helical thickenings (Fig. 2, Table 5). VASCULAR BUNDLES: EPIDERMIS:

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collateral in one row, phloic sclerenchyma more strongly developed, with thicker cell walls than xyloic sclerenchyma, sclerenchyma less prominent around smaller than larger bundles. Bundle sheath cells thin- to somewhat thick-walled forming discontinuous sheaths around larger bundles, continuous around smaller bundles. Stegmata with rough-surfaced, spherical silica bodies present along outer margin of phloic bundle sclerenchyma of midvein and larger lateral bundles; absent around smaller bundles (Table 6). CRYSTALS: raphide bundles in thin-walled idioblasts elongated parallel to the midvein in both palisade and spongy mesophyll; idioblasts larger than adjacent assimilatory cells. Stem. 4-lobed. HAIRS: absent or uniseriate, bi- or tricellular, solitary, glandular, sunken (Fig. 1). STOMATA: absent. CUTICLE: moderately thick, irregular to relatively smooth, with anticlinal striations. EPIDERMIS: cells elliptical, square, or polygonal, thin- to thick-walled. GROUND TISSUE: parenchymatous, zonate or non-zonate. A uniseriate layer of somewhat thick-walled cells subtends the epidermis. In those species with zonate ground tissue, the outer region consists of two kinds of thin-walled cells organized as a reticulum: (1) many, small, living, rounded to polygonal, assimilatory cells among which there are (2) fewer, large, dead, water-storage cells with scalariform to helical wall thickenings (Table 7). Vascular bundles few. In these same species, the inner region consists of a single kind of small, living, round, thin-walled, TABLE 4. Foliar hypodermis and fibre bundles. Ad = adaxial, Ab = abaxial, ser=seriation, Ct = cell type, M = mesophyll, Abs = absent Hypodermis Genus Section

Ad ser

Ab ser

Cadetia Pterocadetia 1 1 Cadetia 1 1 Dendrobium Desmotrichum 1 (2) — Goniobulbon 1 1 Diplocaulobium 1, 2, 3 (4) — Bolbidium 1, 2 3 Rhizobium 1, 2, 3 1, 2 Sarcopodium 1, 2 (3) — Dendrocoryne 1, — 1, — Latouria 1 — Inobulbon 1 1 Callista 1, 2, — 1, 2 Dendrobium — — Platycaulon — — Pedilonum 1, — 1, — Brachyanthe — — Stachyobium — — Phalaenanthe — — Eleutheroglossum 1, — 1, — Spatulata 1, — 1, — Formosae — — Rhopalanthe 1, 2, — 1, 2, — Aporum — 1, 2, 3 Grastidium — — Macrocladium — — Monanthos — — Phalaenanthe/Spatulata 1 1 Pseuderia — —

Fibre bundles Ct

Ad

Ab

M

P P P P PF P P PF P P P P

Abs X X

X X

X

X

P

P P P PF

X X

X X X X X X X X X X X X X X X X X X X X X X

X

X

P X

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TABLE 5. Mesophyll characteristics Homogeneous seriation Genus Section Cadetia Pterocadetia Cadetia Dendrobium Desmotrichum Goniobulbon Diplocaulobium Bolbidium Rhizobium

Heterogeneous seriation Palisade

Spongy

4–9 6–8

5–11 6–9

+, helical cell wall thickenings present +, helical cell wall thickenings present

8–10 5–7

+, except D. comatum, D. pallens, D. plicatile – – + +, helical thickenings only in D. toressae

9–14 4–9 2–4 10–11 15–19, D. pugioniforme; 7–11, D. toressae

Sarcopodium Dendrocoryne Latouria Inobulbon Callista Dendrobium Platycaulon Pedilonum Brachyanthe Stachyobium Phalaenanthe Eleutheroglossum Spatulata Formosae Rhopalanthe Aporum Grastidium Macrocladium Monanthos Phalaenanthe/Spatulata Pseuderia

9–12 7–11 7–15 6–12 5–9 8–14 7–9 7, 8 6–14 16–20 10–12 8–12 14, 15 9–49 6–8 11–14 5–12

Tendency for zonation in most species 1–4 2–5

6–13 6–15

2–4 2–5

7–8 4–8

3–4

8–12

1–3 3–5

6–8 3–9

Water storage cells in mesophyll

– – – +, helical cell wall thickenings present – –, except D. loddigesii – – – – – – – – – + – – – – –

food-storage cell. Vascular bundles many. In those species with non-zonate ground tissue there are only living, rounded to polygonal assimilatory cells and the vascular bundles are distributed randomly throughout the parenchyma. All parenchyma cells may show cruciate starch grains. VASCULAR BUNDLES: collateral, concentrated in inner region of stems with zonate ground tissue, randomly dispersed in stems with non-zonate ground tissue, a single large bundle or bundle group tends to be associated with each lobe of the stem; phloic sclerenchyma more strongly developed and thicker-walled than xyloic sclerenchyma. Stegmata with rough-surfaced, spherical silica bodies occur along outer margin of phloic bundle sclerenchyma. CRYSTALS: raphide bundles in a few thin-walled parenchyma cells of outer region of ground tissue near epidermis. Figures 1–4. Cadetia pomatophila. Fig. 1. Transverse section of pseudobulb showing sunken glandular hair. Opaque material spreading from apex is apparently the exudate, × 2445. Fig. 2. Transverse section of leaf with helical thickening bands of water-storage cell walls photographed through crossed Nicols. × 550. Fig. 3. Dendrobium albosanguineum. Abaxial foliar epidermis scraping showing paracytic stomatal apparatus. × 400. Fig. 4. D. rigidum. Transverse section leaf showing elongated hypodermal cells (hc) and unpleated water-storage cell walls (w). × 290. Scale bars in all figures = 10 µm.

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Root. VELAMEN: 2–5-layered (Table 8), cells polygonal to irregular, anticlinal with fine, helical, anastomosing thickening bands; cells of outermost layer smaller than subtending cells, rectangular to square, mostly periclinal, protists and fungal hyphae frequently present. TILOSOMES: absent. EXODERMIS: walls of dead cells s-, <-, or >-thickened (Table 8), longitudinal walls with tenuous scalariform thickenings; passage cells at irregular intervals. CORTEX: 5–7 cells wide (Table 8), cells mostly rounded, thin-walled, parenchymatous; outermost 1 or 2 layers of cells small, more or less polygonal; innermost single layer of cells small, frequently tangentially flattened; some cells dead, empty, walls conspicuously birefringent; intercellular spaces present. ENDODERMIS: uniseriate, cells more or less isodiametric, cell walls s-thickened opposite phloem sectors, thin opposite xylem sectors (Table 8). PERICYCLE: uniseriate, cell walls s-thickened opposite phloem sectors, thin opposite xylem sectors. VASCULAR CYLINDER: 6-, 8-, or 10-arch (Table 8), conducting strands embedded in sclerenchyma, xylem and phloem segments alternate around the circumference. PITH: sclerenchymatous (Table 8), cells polygonal, central cells somewhat larger and more rounded than peripheral cells; intercellular spaces absent to obscure. CRYSTALS: raphide bundles in unmodified outer cortical cells.

TABLE 6. Stegmata. Leaf Vascular bundles Genus Section Cadetia Pterocadetia Cadetia Dendrobium Desmotrichum Goniobulbon Diplocaulobium Bolbidium Rhizobium Sarcopodium Dendrocoryne Latouria Inobulbon Callista Dendrobium Platycaulon Pedilonum Brachyanthe Stachyobium Phalaenanthe Eleutheroglossum Spatulata Formosae Rhopalanthe Aporum Grastidium Macrocladium Monanthos Pseuderia aabs=fibre

Stem Fibre bundles Adaxial

+ + + + +, except D. rigidum + + + + + +, except D. senile + + + + + + + + + +, absent in D. leonis + + + –

bundles absent

Abaxial absa abs

+, C. taylori only + –

+, C. taylori only + +

abs – +

– +

Vascular bundles

+ abs abs abs abs abs abs abs abs abs abs abs abs abs abs abs abs abs

–

+ +

abs abs +

+ abs

+ + + + +, only D. lichenastrum + + + + + +, except D. senile + + + + + + + + + + + – – –

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Sections Pterocadetia and Cadetia Anatomy of these taxa is essentially similar, but with the following differences: bicellular in Pterocadetia, unicellular in Cadetia; CAULINE HAIRS absent in C. collina, C. obliqua (Pterocadetia), C. hispida (Cadetia); CAULINE GROUND TISSUES zonate in C. collina, C. obliqua (Pterocadetia), non-zonate in C. taylori (Pterocadetia), C. pomatophila, C. hispida (Cadetia); VELAMEN 2–5-layered in Pterocadetia, 3 or 4-layered in Cadetia; EXODERMAL DEAD CELLS s-thickened in C. collina, C. taylori, lacking in our specimen of C. obliqua (Pterocadetia), <-thickened in C. hispida, >-thickened in C. pomatophila (Cadetia); VASCULAR CYLINDER 6- or 10-arch in Pterocadetia, 6- or 8-arch in Cadetia. FOLIAR HAIRS

Generalized anatomy of Dendrobium Leaf surface. HAIRS: uniseriate, uni- to tricellular, solitary, glandular, base sunken in crypt, ambifacial. EPIDERMIS: cells polygonal, anticlinal walls more or less straightsided on both surfaces, curvilinear in many cells, the angles then rounded (Fig. 3). STOMATA: abaxial, basically paracytic (Fig. 3); ranges of means for guard-cell pairs: 24–59 µm long, 21–51 µm wide (Table 3). Dendrobium canaliculatum (section Spatulata) is the only species in this study with amphistomatal leaves. TABLE 7. Water-storage cells in cauline ground tissue Genus Section Cadetia Pterocadetia Cadetia Dendrobium Desmotrichum Goniobulbon Diplocaulobium Bolbidium Rhizobium Sarcopodium Dendrocoryne Latouria Inobulbon Callista Dendrobium Platycaulon Pedilonum Brachyanthe Stachyobium Phalaenanthe Eleutheroglossum Spatulata Formosae Rhopalanthe Aporum Grastidiumb Macrocladiumb Monanthosb Pseuderiab

Pleated

Unpleated

– –

+a +a

+ (pseudobulb) – – – – +a + + +a + + + + + + + + – + + –

– (rhizome) + + + + – – – – – + – – – – – – + – – +

aHelical thickening bands present bWater-storage cells absent.

in walls of some cells.

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Leaf (T.S.). Leaves conduplicate, thin. CUTICLE: thin to thick, smooth to irregular. EPIDERMIS: cells square, rectangular to hexagonal with rounded angles; adaxial cells larger than abaxial; cells thin- to thick-walled, outer walls frequently thickest. STOMATA: superficial, substomatal chambers small, outer ledges large, inner ledges minute. HYPODERMIS: present (Fig. 4) or absent, subtending adaxial or abaxial or TABLE 8. Selected root charactersa Exodermal cell wall thickenings Cortex

Velamen

Cell wall thickenings Genus Section

Se

T

Cadetia Pterocadetia 2–5 Cadetia 3, 4 Dendrobium Desmotrichum 4–8 Goniobulbon 5 Diplocaulobium 2–5 Bolbidium 4, 5 Rhizobium 2–7 Sarcopodium 2–3 Dendrocoryne 3–11 Latouria 6–9 Inobulbonc Callista 4–14 Dendrobium 3–11 Platycaulon 4–8 Pedilonum 3–8 Brachyanthe 5–7 Stachyobium 4, 5 Phalaenanthe 5, 6 Eleutheroglossum 7–12 Spatulata 6–12 Formosae 4–17 Rhopalanthe 4–7 Aporum 4–6 Grastidium 5–8 Macrocladium 4–6 Monanthos 4 Phalaenanthe/ Spatulata 9, 10 Pseuderia 2, 3

V

O

– –

– –

+

– – + – – + – –

– – – – +/– + +/– +

+ + +

– – – – – – – – – – – – + – +

– + +/– +/– – – – – – – – – – – +

+ + + + + +

– –

– –

∪

∩

+ +

Se

O

+ +

+/– 5–7 +/– 5–6

+ +

+ + + +

+/– + + + + +/– _ –

4–9 5–6 4–6 4–6 5–12 6–8 6–12 7–9

+ + + + + + + +

– 5–10 +/– 4–8 – 6, 7 – 4–9 – 5, 6 – 5,6 +/ ?b – 6–9 – 6–9 +/– 5–9 – 5–8 – 4–7 – 11–18 – 12–14 – 17–19

+ + + + + + + + + + + + + + +

+ + + + + +

+ +

+ + +

+ + + + + + +

+

+ + +

+

L

– –

Xylem sectors

Endodermis

6, 7 + 8–11 +

∪

L

Cell orientation A

P

– –

+

+

– +/– + + +/– +/– +/– _ + –

+

– +/– – – – – – – – – – – – – –

+ +

– +

Pith

+ + + +

+

+

+

6, 10 6, 8

+ +

+

9–17 7 9, 10 8 5–19 16–20 9–19 14–17

+ + + + +

8–16 6–24 10, 12 7–16 9, 11 5, 6 ?b 11, 15 18, 21 8–18 9, 21 6–9 27 10, 11 15

+ + + + + + ?b +

+ + + + + + + + + + + + + +

+ + + + + +

S

+ +

+

+ +/– + +

I

+

+ + +

10 11, 18

P

+

+ + + + + + + +

+ + + + + + +

aSe=seriation, T=tilosomes, V=V-thickened innermost velamen cell layer, O=O-thickened cell walls, ∪=∪-thickened cell walls, ∩=∩-thickened cell walls, L=laminated, A=anticlinal, P=periclinal, I=isodiametric, S=sclerenchymatous, P=parenchymatous. b?=data missing. c=root lacking.

Figures 5–8. Fig. 5. Dendrobium acinaciforme. Transverse section of leaf showing alternating larger and smaller abaxial fibre bundles (fb). Outer fibres of larger bundles are thicker-walled than inner fibres. ×495. Fig. 6. D. albosanguineum. Longitudinal section leaf with row of stegmata containing spherical, roughsurfaced silica bodies adjacent to vascular bundle fibres (left). ×880. Fig. 7. D. jonesii. Transverse section pseudobulb ground tissue with vascular bundles, unpleated water-storage cells (w) among parenchyma cells. ×250. Fig. 8. D. pachyphyllum. Transverse section root showing helical thickening bands of velamen cell walls (v) and <-thickened exodermal cell walls (e). ×1060. Scale bars in all figures = 10 µm.

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both surfaces, comprising one or more layers of polygonal to rounded, thin-walled parenchyma cells or parenchyma cells alternating with fibre bundles (Table 4). FIBRE BUNDLES: present (Fig. 5) or absent, with or without stegmata all of which contain rough-surfaced spherical silica bodies (Table 6). CHLORENCHYMA: homogeneous or heterogeneous, cells living, columnar, polygonal, oval, or rounded, thin-walled; intercellular spaces more conspicuous abaxially; water-storage cells usually lacking (Table 5). VASCULAR BUNDLES: collateral, in one row, sclerenchyma well-developed, associated with both xylem and phloem poles. Bundle sheath cells thin-walled, forming discontinuous sheaths around most bundles, continuous around smaller bundles. Stegmata all with rough-surfaced, spherical silica bodies along outer margin of sclerenchyma (Fig. 6) of larger bundles at either xylem or phloem poles, or both; absent around smaller bundles, and generally only at the phloic side of midvein bundles (Table 6). CRYSTALS: raphide bundles in thin-walled mesophyll idioblasts elongated parallel to the midvein; these markedly larger than adjacent assimilatory cells. Stem. HAIRS and STOMATA: absent. CUTICLE: moderately thick, smooth. EPIDERMIS: cells square, rectangular, hexagonal, or rounded; thick-walled. GROUND TISSUE: zonate, outer 1–several layers comprise somewhat to very thick-walled, polygonal parenchyma cells. Inner region comprises 2 classes of cells: (1) smaller, living, rounded to polygonal, thin-walled assimilatory parenchyma forming a network around vascular bundles among which are (2) scattered, larger, dead, thin-walled water-storage cells often with pleated outlines, with or without helical thickening bands (Fig. 7, Table 7); intercellular spaces present; cruciate starch grains in assimilatory cells. VASCULAR BUNDLES: collateral, scattered, outer bundles smaller than inner bundles; bundle sclerenchyma mostly phloic, some at xylem poles of larger bundles. Stegmata all with rough-surfaced, spherical silica bodies along outer margin of phloic bundle sclerenchyma, sometimes associated with both phloic and xyloic sclerenchyma. CRYSTALS: raphide bundles in rounded, thin-walled parenchyma cells of ground tissue. Root. VELAMEN: 2–17-layered (Table 8), cells of outermost layer somewhat smaller than subtending cells, square or rectangular, and either periclinal or anticlinal; inner cells polygonal to irregular or rounded, anticlinal, with slender to relatively wide helical anastomosing thickening bands (Fig. 8); hairs, hyphae, and protists frequently present. TILOSOMES: usually absent (Table 8). EXODERMIS: walls of dead cells s-, >-, or <-thickened (Fig. 8, Table 8), longitudinal walls with tenuous scalariform thickenings; thin-walled passage cells occur at irregular intervals. CORTEX: 4–14 (and 17–19) cells wide (Table 8); cells rounded to oval, thin-walled, parenchymatous; cells of outermost 1 or 2 layers small, more or less polygonal; cells of innermost 1 or 2 layers frequently tangentially flattened; intercellular spaces present. ENDODERMIS: uniseriate, cell walls s-thickened opposite phloem sectors, thin opposite xylem sectors (Fig, 9, Table 8). PERICYCLE: uniseriate, cell walls s-thickened opposite phloem sectors, thin opposite xylem sectors. VASCULAR CYLINDER: 5- to 27-arch (Table 8), conducting strands embedded in sclerenchyma, xylem and phloem segments alternate around the circumference. PITH: sclerenchymatous throughout, pith cells then merging with sclerenchyma surrounding vascular elements, cells thickwalled, polygonal, intercellular spaces absent or obscure, or parenchymatous, cells thin- to sometimes thick-walled, rounded to circular, distinct from vascular sclerenchyma, intercellular spaces evident (Table 8); cruciate starch grains in

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parenchymatous pith cells common. CRYSTALS: raphide bundles in unmodified outer cortical cells, or in modified thin-walled, elongate, saccate cells of the middle cortical region. Section Desmotrichum Species examined. D. angustifolium, D. comatum, D. macraei, D. pallens, D. pardalinum, D. plicatile, D. xantholeucum. Leaf surface. HAIRS: bicellular, tricellular in D. angustifolium and D. pallens (MO); walls of 2 crypt cells adjacent to basal hair cell thickened, conspicuously birefringent in D. angustifolium, D. macraei, D. pallens. Leaf (T.S.). CUTICLE: mostly moderately thick to thick, but thin to moderately thick in D. pallens (MO) and D. xantholeucum, smooth in D. comatum (SEL) and D. plicatile to relatively smooth and somewhat irregular in all other species. EPIDERMIS: upper cells approximately same size as lower cells; cells thin-walled. STOMATA: slightly sunken, outer ledges rather large, inner ledges larger than in all other Dendrobiinae. HYPODERMIS: adaxial only, well-defined in D. angustifolium, D. macraei, D. pardalinum, and D. xantholeucum, 1-layered, occasionally 2-layered, comprising 2 types of cells: (1) polygonal to irregular, living, thin-walled, periclinally oriented parenchyma cells and (2) irregularly shaped apparently dead cells with thin, strongly birefringent walls that are sometimes pleated (e.g. D. angustifolium); vaguely distinguishable in all other species comprising a single cell type of rather large, somewhat polygonal to rounded, thin-walled parenchyma cells anticlinally oriented toward midvein and with fewer chloroplasts than subtending mesophyll cells. FIBRE BUNDLES: absent in D. comatum; 1 row of abaxial fibre bundles present in all other species, thicker-walled peripheral fibres in D. plicatile and especially in D. xantholeucum; stegmata present. CHLORENCHYMA: homogeneous, 9–14 layers, cells of 2 types in all species: (1) cells living, thin-walled, polygonal to oval (long axis periclinal) to irregular and rounded forming a network around (2) larger, empty, dead, irregularly shaped water-storage cells, except D. comatum, D. pallens, and D. plicatile, where all cells are living, thin-walled, polygonal to oval to rounded. Birefringent, anastomosing thickening bands present on walls of many mesophyll cells in D. pallens, D. pardalinum, and D. plicatile. VASCULAR BUNDLES: sclerenchyma rather poorly developed at xylem pole of midvein in D. xantholeucum. Some bundle sheath cells thick-walled in D. macraei, D. pallens, D. pardalinum, D. plicatile, and D. xantholeucum. CRYSTALS: druses rare in some upper mesophyll assimilatory cells in D. angustifolium. Pseudobulb. CUTICLE: thick in D. angustifolium and D. macraei, moderately thick in D. pardalinum and D. xantholeucum. EPIDERMIS: cells mostly periclinal, relatively thinwalled in D. angustifolium, D. pardalinum, and D. xantholeucum, thick-walled, inconspicuously laminated in D. macraei. GROUND TISSUE: water-storage cell outlines pleated in D. angustifolium and D. pardalinum. VASCULAR BUNDLES: lacunae occur in the ground tissue immediately adjacent to the phloic sclerenchyma of many bundles (Fig. 10). Rhizome. CUTICLE: moderately thick in D. macraei and D. xantholeucum, moderately thick to thick in D. comatum (SEL), and thick in D. angustifolium. EPIDERMIS: cells periclinal or anticlinal, very thick-walled and laminated in D. comatum (SEL), D.

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macraei, D. pallens (MO), and D. xantholeucum; cell walls somewhat thickened but unlaminated in D. angustifolium. GROUND TISSUE: water-storage cell outlines unpleated. Cruciate starch grains in assimilatory cells of D. comatum (SEL), D. macraei, and D. pallens (MO). VASCULAR BUNDLES: Sclerenchyma associated with both phloem and xylem poles in D. angustifolium, mostly with phloem pole in D. comatum (SEL), D. pallens (MO), D. macraei, and D. xantholeucum; sclerenchyma much less well-developed and thinner-walled at xylem poles in D. macraei and D. xantholeucum. Root. VELAMEN: 4–8-layered, cells variously anticlinal, innermost cells directed more anticlinally than outer cells in D. macraei, D. pallens (K), and D. plicatile; fine anastomosing thickening bands present, these nearly anticlinal in innermost layer of cells; anastomosing thickening bands in these cells mostly periclinal, very conspicuous in D. comatum. EXODERMIS: dead cell walls s-thickened, outer tangential and anticlinal walls especially thickened in D. macraei, laminated in D. comatum (K), D. macraei, D. pallens (K), D. pardalinum, and D. plicatile; longitudinal walls of dead cells with tenuous scalariform thickenings and oval-bordered pits. CORTEX: 4–9 cells wide; a few scattered cells dead, empty, walls conspicuously birefringent in D. comatum, D. macraei, and D. xantholeucum; some cells with birefringent anastomosing thickening bands in D. macraei, D. pardalinum and D. plicatile. ENDODERMIS: cells more or less isodiametric, cell walls laminated in D. comatum (K), D. pardalinum, and D. plicatile. VASCULAR CYLINDER: 9-, 13-, 14-, 15-, or 17-arch. PITH: sclerenchymatous in D. comatum (K), D. macraei, D. pardalinum, and D. xantholeucum; parenchymatous in D. plicatile, D. comatum (SEL), and D. pallens (K). CRYSTALS: cortical raphide bundles in D. comatum, D. plicatile, and D. xantholeucum.

Section Goniobulbon Species examined. D. chrysotropis. Leaf surface. thickened.

HAIRS:

bicellular, walls of 2 crypt cells adjacent to basal hair cell

Leaf (T.S.). CUTICLE: moderately thick to thin in some abaxial cells, smooth on adaxial surface; irregular on abaxial surface. EPIDERMIS: cells thin-walled. HYPODERMIS: adaxial, 1-layered, cells living, somewhat polygonal to columnar-oval (above midvein); very weakly distinguishable abaxially, 1-layered, cells living, somewhat polygonal to rounded, thin-walled. FIBRE BUNDLES: absent. CHLORENCHYMA: heterogeneous; palisade (4) 6–8 (9) cells, columnar to columnar-oval; spongy 7–9 cells, somewhat polygonal to oval; intercellular spaces few and small. VASCULAR BUNDLES: large and small bundles alternate regularly; some bundle sheath cells thickwalled, some showing birefringent anastomosing thickening bands. Figures 9–12. Fig. 9. Dendrobium salaccense. Transverse section root showing s-thickened endodermal cell walls (en), endodermal passage cells (p) opposite xylem strands, alternating strands of xylem and phloem (ph), and large metaxylem cells (m). × 500. Fig. 10. D. macraei. Transverse section pseudobulb with phloem segment (ph) of vascular bundle adjacent to lacuna (1). × 515. Fig. 11. D. pachyphyllum. Transverse section leaf illustrating pleated cell walls of water-storage cells. × 475. Fig. 12. D. schoeninum. Transverse section root with V- and <-thickened walls of innermost cells of velamen (v) adjacent to exodermis (e). The inked line outlines the limits of a velamen cell within which the thickening forms. × 1030. Scale bars = 10 µm.

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Stem. EPIDERMIS: cell walls very thick, laminated. GROUND TISSUE: Water-storage cell outlines unpleated. Root. VELAMEN: 5-layered, cells with fine thickening bands; outermost cells mostly periclinal. EXODERMIS: walls of dead cells s-thickened, faintly laminated. CORTEX: 5 or 6 cells wide. PERICYCLE: uni- to biseriate. VASCULAR CYLINDER: 7-arch. PITH: sclerenchymatous, cell walls unlaminated. Section Diplocaulobium Species examined. D. arachnoideum, D. fariniferum, D. guttulatum. Leaf surface. HAIRS: bicellular, walls of 2 cells of crypt adjacent to basal cell of hair thickened, birefringent. Leaf (T.S.). CUTICLE smooth; adaxial surface of D. arachnoideum thick, abaxial moderately thick; adaxial surface of D. guttulatum thin to moderately thick, abaxial surface thin. EPIDERMIS: cells thin-walled. HYPODERMIS: adaxial 2 or 3 (-4)-layered in D. arachnoideum, 1-layered in D. guttulatum; sections lacking for D. fariniferum. FIBRE BUNDLES: D. arachnoideum, adaxial — 2 (3) staggered series, fibres evenly thick-walled, lacking stegmata; clusters of 2 or 3 and solitary fibres scattered in palisade mesophyll; abaxial — 1 series, outer fibres thicker-walled than inner, stegmata present; clusters of 2–3 and solitary fibres scattered in spongy mesophyll; fibre clusters frequently fuse with vascular bundle sclerenchyma; D. guttulatum, adaxial — 1 series of multicellular bundles alternate with vascular bundles occasionally fusing with bundle sclerenchyma, lacking stegmata; abaxial — 1 series of few-celled bundles or solitary fibres alternate with vascular bundles, stegmata present. Tissues lacking for D. fariniferum. CHLORENCHYMA: heterogeneous, palisade 2–4 and 2 or 3 cells in D. arachnoideum and D. guttulatum, respectively; cells mostly polygonal in D. guttulatum, columnar in D. arachnoideum, spongy 5–7 cells in both species; cells polygonal to rounded. VASCULAR BUNDLES: sclerenchyma well-developed at both xylem and phloem poles of midvein and largest lateral bundles. Bundle sheath cells thin- or thick-walled around the same vascular bundle, forming discontinuous sheaths around most bundles. Pseudobulb. CUTICLE: moderately thick to thick. EPIDERMIS: cells thin-walled. GROUND water-storage cell outlines unpleated.

TISSUE:

Rhizome. CUTICLE: moderately thick to thick. GROUND TISSUE: in D. arachnoideum only, outer 2 or 3 cell layers free of vascular bundles and comprise mostly thin-walled chlorenchyma; remaining ground tissue of living, very rounded, thin-walled parenchyma cells, and in D. guttulatum there are also a few somewhat larger, mostly rounded, dead cells with conspicuously birefringent walls. VASCULAR BUNDLES: sclerenchyma associated with xylem poles of many bundles, fibres usually thinnerwalled than in phloic sclerenchyma. Root. VELAMEN: 2–5-layered; innermost layer of cells in D. fariniferum conspicuously thick-walled. TILOSOMES: present in D. fariniferum and D. arachnoideum, absent in D. guttulatum. EXODERMIS: dead cells s-thickened, outer and radial walls conspicuously so; walls laminated; all species with tenuous scalariform wall thickenings, ovalbordered pits also in D. arachnoideum. CORTEX: 4–6 cells wide; scattered raphide idioblasts enlarged, irregularly shaped, with birefringent walls; walls of some cells

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with birefringent anastomosing thickening bands in D. arachnoideum and D. guttulatum. ENDODERMIS: cell walls faintly laminated in D. fariniferum. PERICYCLE: uni- to biseriate. VASCULAR CYLINDER: 9- or 10-arch. PITH: sclerenchymatous. CRYSTALS: raphide bundles in both modified and unmodified cortical idioblasts. Section Bolbidium Species examined. D. pachyphyllum. Leaf surface.

HAIRS:

bicellular.

STOMATA:

tetracytic and cyclocytic.

Leaf (T.S.). CUTICLE: thin. STOMATA: outer ledges medium. HYPODERMIS: adaxial, 1 or 2 layers of small rounded to polygonal to oval cells, periclinal, thin-walled; abaxial, 3 layers of small, thin-walled cells, outer layer oval, periclinal, middle layer rounded, inner layer oval, anticlinal. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 14- or 15-layered, cells mostly oval, cruciate starch grains present; ad- and abaxial subdermal chlorenchyma cells significantly smaller than other chlorenchyma cells of the mesophyll; water-storage cells with very sinuous, pleated outlines near and above midvein (Fig. 11). Stem. CUTICLE: moderately thick to thick. GROUND TISSUE: zonate, water-storage cell outlines unpleated. Root. VELAMEN: 4- or 5-layered, anastomosing helical bands relatively thick; innermost layer of cells conspicuously anticlinal. EXODERMIS: dead cell walls <-thickened, laminated, tenuous scalariform thickenings and oval-bordered pits in longitudinal walls of dead cells. CORTEX: 4–6 cells wide. ENDODERMIS: cells anticlinal, some walls laminated. PERICYCLE: uni- to biseriate. VASCULAR CYLINDER: 8-arch. PITH: sclerenchymatous, cell walls laminated. CRYSTALS: raphides in unmodified cortical cells. Section Rhizobium Species examined. D. cucumerinum, D. lichenastrum, D. linguiforme, D. pugioniforme, D. rigidum, D. schoeninum, D. teretifolium, D. toressae, D. wassellii. Leaf. Leaves in section Rhizobium have been described in detail in Stern et al. (1994). Stomatal configurations are basically tetracytic, but some cyclocytic arrangements with five or more subsidiary cells also occur. Leaves are thick, fleshy or leathery and hard, often terete or almost so. The exposed epidermis is abaxial, but in a few species, in addition to the abaxial epidermis, a small amount of adaxial epidermis is also exposed in a foliar groove. In those leaves covered entirely by abaxial epidermis, the adaxial epidermis is still present, but immersed within and surrounded by the mesophyll. It flanks the walls of an internal canal represented as a lacuna on cross sections. The bilaterally symmetrical arrangement of the vascular bundles, a characteristic of all examined leaves in section Rhizobium, divides the leaf into equilateral halves, the canal being centred along the mid-plane. Xylem of all vascular bundles faces the mid-plane of the leaf. Stegmata lacking in D. rigidum. Stem.

CUTICLE:

Thick in D. rigidum and D. lichenastrum, thin in D. toressae.

EPIDERMIS:

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cells hexagonal, pentagonal, square, outer walls domed, papillate, and spired, walls somewhat thick, laminated in D. rigidum; cells pentagonal, square, rectangular, outer walls rounded, walls thin in D. lichenastrum; cells square, rectangular, outer walls rounded, walls thin in D. toressae. GROUND TISSUE: zonate; outermost layer 1 (2) cell wide, cells mostly anticlinal, rectangular, walls very thick, laminated, subtending layer 7–12 cells wide, scattered thick-walled unpleated water-storage cells surrounded by rounded, thin-walled assimilatory cells that are continuous with similar tissue in the core of the stem in D. rigidum; outermost layer 1 cell wide, cells square, pentagonal, rectangular, walls slightly thick, subtending layer 8–10 cells wide, scattered thick-walled, unpleated water-storage cells surrounded by rounded thickwalled assimilatory cells that are continuous with distinctly smaller-sized cells of similar form in the core of the stem in D. lichenastrum; outermost layer 5–8 cells wide, cells rounded, distinctly larger than those of the subtending layer, walls thin, contiguous groups of angular water-storage cells present, subtending layer 3–5 cells wide, few scattered thick-walled, unpleated water-storage cells present among thinwalled, parenchyma cells that are continuous with those of the core tissue in D. toressae. VASCULAR BUNDLES: forming a ring of bundles joined by contiguous sclerenchyma, the ring surrounding central scattered bundles in D. rigidum and D. toressae; bundles scattered throughout in D. lichenastrum. Stegmata present only in D. lichenastrum. CRYSTALS: raphide bundles and druses in rounded, thin-walled parenchyma cells of ground tissue in D. lichenastrum. Root. VELAMEN: 2–7-layered mostly conspicuously anticlinal in D. cucumerinum, D. linguiforme, D. rigidum, D. schoeninum, and D. wassellii; somewhat anticlinal in D. lichenastrum and D. toressae, with fine anastomosing thickening bands, outermost layer of cells smaller than subtending cells, square, mostly slightly anticlinal in D. cucumerinum, D. linguiforme, and D. wassellii; outermost layer of cells approximately same size as subtending cells, square, and either periclinal or anticlinal in D. toressae; outermost layer of cells as large as or larger than subtending cells, polygonal, and somewhat to conspicuously anticlinal in D. lichenastrum; outermost layer of cells larger than subtending cells, mostly rectangular and conspicuously anticlinal in D. rigidum and D. schoeninum, cells of innermost layer smaller than those they subtend, polygonal, anticlinal in D. linguiforme and D. wassellii, V-thickened to <- or s-thickened in D. cucumerinum, D. schoeninum (Fig. 12), and D. toressae, not V-thickened in D. lichenastrum; walls laminated in D. schoeninum and D. cucumerinum. EXODERMIS: dead cells >-thickened, walls laminated in D. cucumerinum, D. rigidum, D. schoeninum, D. toressae, and D. wassellii; dead cell walls O-thickened, walls laminated in D. lichenastrum and D. linguiforme. CORTEX: 5–7 and 9–12 cells wide; cells rounded to somewhat polygonal; a few scattered cortical cells dead, empty, irregularly shaped; walls conspicuously birefringent in D. cucumerinum, D. schoeninum, D. toressae, and D. wassellii; cruciate starch grains in cells of D. lichenastrum, D. toressae, and D. wassellii. ENDODERMIS: cells more or less isodiametric, except anticlinal in D. cucumerinum, D. linguiforme, and D. schoeninum; cell walls laminated in D. lichenastrum, D. linguiforme, D. rigidum, and D. wassellii. VASCULAR CYLINDER: 5-, 8-, 11-, 13-, 17-, or 19-arch. PITH: sclerenchymatous in D. lichenastrum and D. toressae; parenchymatous in all remaining species, cells somewhat thick-walled in D. rigidum; starch grains in pith cells of D. wassellii. CRYSTALS: raphide bundles in unmodified outer cortical cells; and in thinwalled, elongate, saccate idioblasts in the middle region of the cortex in D. cucumerinum and D. wassellii; druses in scattered cortical cells of D. wassellii.

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Section Sarcopodium Species examined. D. amplum, D. cymbidioides, D. lyonii. Leaf surface. HAIRS: bicellular, solitary or paired; cell walls of 2 cells of crypt adjacent to basal cell of hair with birefringent thickening. STOMATA: abaxial, paracytic in Dendrobium lyonii, paracytic or tetracytic in D. cymbidioides, basically tetracytic in D. amplum, some anisocytic. Leaf (T.S.) CUTICLE: moderately thick — thin to moderately thick abaxially in D. cymbidioides, moderately thick to thick both surfaces in D. lyonii — smooth adaxially, irregular abaxially. EPIDERMIS: cells polygonal, adaxial cells conspicuously larger than abaxial cells in D. lyonii; cells thin-walled in D. amplum, with thin inner tangential and anticlinal walls and thick, laminated outer tangential walls of both surfaces in D. lyonii, thick-walled in D. cymbidioides, the outer tangential wall inconspicuously laminated; cell lumina of all three species frequently occluded with safranin-staining material. STOMATA: slightly sunken. HYPODERMIS: adaxial in D. cymbidioides, 1 or 2 (3) layers, cells slightly anticlinal, thin-walled, polygonal to somewhat rounded, nuclei present, chloroplasts not evident as in subtending palisade; hypodermal cells alternate with fibre bundles. FIBRE BUNDLES: present adaxially in D. cymbidioides, cells uniformly thick-walled, stegmata present; absent in D. amplum and D. lyonii. CHLORENCHYMA: heterogeneous; palisade cells polygonal to oval (to columnar in D. amplum), thin-walled cells of spongy mesophyll somewhat polygonal to oval to rounded, thin-walled. VASCULAR BUNDLES: sclerenchyma fairly well-developed (not hippocrepiform) over both xylem and phloem poles of midvein and larger lateral vascular bundles in D. amplum, most well-developed (cells thickest-walled) at phloem pole of midvein (sclerenchyma cap hippocrepiform) and of lateral vascular bundles in D. cymbidioides and D. lyonii, but clusters of fibres continuous with the xylem of many lateral vascular bundles in D. amplum and D. lyonii significantly extending xylary tissue adaxially. Bundle sheath cells thin-walled or somewhat thick-walled; birefringent anastomosing thickening bands in walls of some cells. CRYSTALS: raphide bundles infrequent in mesophyll. Stem. CUTICLE: thick, smooth. EPIDERMIS: cells square to rectangular, very thickwalled, laminated. GROUND TISSUE: outer region comprising 1–3 layers of periclinally flattened parenchyma cells with very thick laminated cells in turn subtended by 2 or 3 layers of periclinally flattened, somewhat thick-walled parenchyma cells; some water-storage cell outlines pleated, others with helical thickening bands. Root. VELAMEN: 2 (3)-layered, inner layer cells columnar, conspicuously anticlinal, walls V-thickened internally, anticlinal thickening bands fine, conspicuous; outer layer cells much smaller than subtending cells, square, only somewhat periclinal or anticlinal. TILOSOMES: present, adjacent to passage cells of exodermis. EXODERMIS: dead cells basically s-thickened in D. amplum and D. lyonii, mostly >-thickened with laminated walls in D. cymbidioides. CORTEX: 6–8 cells wide; innermost single (2 in D. amplum) layer(s) of cells small, some scattered cells rounded, empty, dead, with strongly birefringent walls. ENDODERMIS: cells more or less isodiametric, walls laminated in D. cymbidioides. VASCULAR CYLINDER: 16-, 17-, or 20-arch. PITH: parenchymatous. CRYSTALS: raphide bundles in both modified and unmodified cortical cells; modified cells elongate, saccate, thin-walled.

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Section Dendrocoryne Species examined. D. jonesii, D. kingianum, D. macropus, D. speciosum, D. tetragonum. Leaf surface. HAIRS: bicellular, cells lining crypt with strongly birefringent walls in D. speciosum and D. tetragonum and with anastomosing thickening bands in D. speciosum. Leaf (T.S.). CUTICLE: thin to moderately thick in D. kingianum and D. tetragonum, moderately thick in other species, smooth on adaxial surface in all species, smooth on abaxial surface in D. kingianum, D. macropus, and D. tetragonum, mostly smooth in D. jonesii, irregular (undulating) on abaxial surface in D. speciosum. EPIDERMIS: cells square to somewhat rounded to hexagonal, thin-walled in all species, outer walls somewhat thicker than other walls in D. kingianum and D. tetragonum. HYPODERMIS: absent, except 1-layered in D. speciosum where adaxial and abaxial hypodermises are marginally distinct comprising small, living, somewhat polygonal, thin-walled parenchyma cells. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous in D. kingianum and D. macropus 9 or 10 and 10–12 layers, respectively; heterogeneous in D. jonesii, D. speciosum, and weakly in D. tetragonum, palisade 3–5 cells wide, cells somewhat polygonal to oval; spongy mesophyll 6–15 cells wide, cells mostly rounded, but somewhat polygonal to oval in D. speciosum and D. tetragonum; intercellular spaces few and small in spongy mesophyll. VASCULAR BUNDLES: in one row in all species except in two series in D. speciosum. Sclerenchyma well-developed at both xylem and phloem poles of all bundles, except D. speciosum where sclerenchyma is well-developed at both xylem and phloem poles of midvein and adaxial bundles but mostly only welldeveloped at phloem poles of abaxial bundles. Bundle sheath cells mostly thin-walled in D. kingianum and D. macropus, either thin-walled or thick-walled in D. jonesii, D. speciosum, and D. tetragonum; some bundle sheath cells in all species with birefringent anastomosing thickening bands. Stem. CUTICLE: moderately thick to thick in D. macropus and D. tetragonum, very thick in D. jonesii. EPIDERMIS: cell walls very thick, laminated. GROUND TISSUE: outer region comprising 1 layer of very thick-walled, laminated polygonal parenchyma cells in turn subtended by 1–3 layers of thick-walled polygonal parenchyma cells in D. jonesii and D. tetragonum; subtending the epidermis in D. macropus are 3 layers of thick-walled polygonal parenchyma cells. Water-storage cell outlines pleated. Root. VELAMEN: 3 or 4, and 6–11-layered, mostly somewhat anticlinal in all species, conspicuously anticlinal in D. jonesii; cells in all species with fine, helical, anastomosing thickening bands; outermost layer of cells square, either periclinal or anticlinal in D. jonesii and D. speciosum, mostly periclinal in D. kingianum, mostly somewhat anticlinal in D. macropus; outermost layer of cells same size or somewhat larger than subtending cells, rectangular to polygonal, mostly conspicuously anticlinal in D. tetragonum; walls of innermost layer of cells V- to <-thickened in D. jonesii, D. kingianum, and D. tetragonum, sometimes s-thickened in D. jonesii and D. tetragonum. EXODERMIS: dead cells s-thickened in D. kingianum, D. macropus, D. speciosum, and D. tetragonum; longitudinal walls of dead cells with oval-bordered pits in D. kingianum and D. tetragonum. CORTEX: 6–12 cells wide; cells rounded, thin-walled, innermost 1–2 layers of cells mostly rounded in D. kingianum; a few scattered cells dead, empty, irregularly shaped, with conspicuously birefringent walls in D. jonesii, D. kingianum, D. speciosum, and D. tetragonum; strongly birefringent anastomosing thickening bands in some cortical cell walls in D. jonesii, D. macropus, and D. speciosum;

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cruciate starch grains in some cortical cells in D. kingianum and D. speciosum. ENDODERMIS: cells more or less isodiametric in D. kingianum and D. speciosum, anticlinal in D. jonesii and D. tetragonum, periclinal in D. macropus. VASCULAR CYLINDER: 9-, 14-, 15-, or 19-arch; conducting strands in D. jonesii only partially embedded in thick-walled sclerenchyma cells, these extend centripetally halfway around phloem sectors but just to the outer edge of xylem sectors, sclerenchyma is subtended by thinwalled parenchyma cells; a few small, thick-walled cells encircle larger xylem elements. PITH: parenchymatous, all cells rounded in D. kingianum, D. macropus, D. speciosum, and D. tetragonum; parenchymatous, outer cells polygonal, lacking intercellular spaces, inner cells rounded to circular with intercellular spaces in D. jonesii, intramedullary xylem present (?). CRYSTALS: raphide bundles in unmodified outer cortical cells in D. jonesii, D. speciosum, and D. tetragonum.

Section Latouria Species examined. D. johnsoniae, D. macrophyllum. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: mostly moderately thick, smooth on adaxial surface, rugose abaxially. EPIDERMIS: cells square, rectangular to pentagonal, thin-walled. HYPODERMIS: weakly defined beneath adaxial epidermis in D. johnsoniae, 1-layered, cells mostly anticlinal, thin-walled but somewhat thicker than walls of subtending mesophyll cells, polygonal to rounded, empty. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, cells polygonal to oval to rounded. CRYSTALS: Druses in mesophyll cells of D. macrophyllum. Stem.

EPIDERMIS:

cells square to pentagonal, very thick-walled, laminated. GROUND outer region in D. johnsoniae comprising 4 layers of somewhat thick-walled polygonal parenchyma cells; in D. macrophyllum, there 2 or 3 layers of somewhat thickwalled polygonal parenchyma cells. Water-storage cell outlines conspicuously pleated. CRYSTALS: raphide bundles are especially common near peripheral vascular bundles in D. macrophyllum. TISSUE:

Root. VELAMEN: 6–9-layered, cells polygonal to irregular, with slender, helical, anticlinally anastomosing thickening bands; outermost layer of cells rectangular, periclinal; innermost layer of cells very elongated anticlinally, V- to <-thickened. EXODERMIS: walls of dead cells >-thickened in D. johnsoniae, s-thickened in D. macrophyllum, unlaminated. CORTEX: 7–9 cells wide. ENDODERMIS: cells more or less isodiametric. VASCULAR CYLINDER: 14-, 17-, or 20-arch, conducting strands embedded in sclerenchyma, this weakly developed in D. johnsoniae. PITH: sclerenchymatous in D. macrophyllum; parenchymatous in D. johnsoniae. CRYSTALS: raphide bundles present in D. johnsoniae.

Section Inobulbon Species examined. D. munificum. Leaf surface.

HAIRS:

bicellular, some unicellular, more numerous on abaxial surface.

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Leaf (T.S.). CUTICLE: thick adaxially, moderately thick to thick abaxially, irregularly undulating. EPIDERMIS: cells mostly somewhat anticlinal, especially adaxially, somewhat thick-walled. STOMATA: slightly sunken. HYPODERMIS: present adaxially 1-layered, cells thin-walled, smaller than subtending palisade cells, living, polygonal, and slightly anticlinal; abaxial hypodermis more weakly defined, 1-layered, cells thinwalled, smaller than subtending cells of spongy mesophyll, living, rounded to somewhat polygonal. FIBRE BUNDLES: absent. CHLORENCHYMA: weakly heterogeneous; palisade 2–4 cells wide, cells polygonal to oval, thin-walled, some cells only somewhat anticlinal; spongy mesophyll 7 or 8 cells wide, cells somewhat polygonal to rounded, thin-walled; abundant scattered water-storage cells in both spongy and palisade regions empty, dead, thin-walled with helical, secondary cell wall thickenings. VASCULAR BUNDLES: sclerenchyma fairly well-developed at both xylem and phloem poles of midvein and larger lateral bundles, cells somewhat thickerwalled at phloem pole. Stem. CUTICLE: very thick. EPIDERMIS: cells square to rectangular, slightly anticlinal, very thick-walled, outer tangential and anticlinal walls >-thickened, laminated. GROUND TISSUE: outer region consists of 3–5 layers of somewhat thick-walled polygonal parenchyma cells subtending the epidermis; some irregularly shaped water-storage cells of the inner region with helical thickening bands, others with pleated outlines; intercellular spaces minute. Root. Unavailable for study. Section Callista Species examined. D. amethystoglossum, D. chrysotoxum, D. densiflorum, D. griffithianum, D. lindleyi, D. palpebrae, D. thyrsiflorum. Leaf surface. HAIRS: bicellular some unicellular in D. lindleyi, solitary, sometimes paired in D. palpebrae. Leaf (T.S.). CUTICLE: thin in most species, moderately thick adaxially in D. densiflorum and D. griffithianum, but thin abaxially, smooth except irregular and undulating D. chrysotoxum. EPIDERMIS: cells thin-walled in D. amethystoglossum, D. griffithianum, D. lindleyi, and D. palpebrae, somewhat thicker-walled in D. densiflorum and D. thyrsiflorum; thick-walled in D. chrysotoxum. HYPODERMIS: absent in D. amethystoglossum; adaxial conspicuous in D. chrysotoxum, 1-layered, cells living, oval to somewhat polygonal and anticlinal, walls thicker than those of subtending mesophyll cells; weakly defined in all other species, 1-layered but 1- or 2-layered in D. thyrsiflorum, cells living, oval to polygonal and mostly periclinal, walls somewhat thicker than those of subtending meosphyll cells; abaxial, weakly defined in all species, 1-layered in D. chrysotoxum, D. densiflorum, D. palpebrae, and D. thyrsiflorum, 1- or 2-layered in D. lindleyi, 2-layered in D. griffithianum. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous in D. amethystoglossum, D. densiflorum, D. palpebrae, and D. thyrsiflorum, 7–10- and 12–15-layered, cells somewhat polygonal to oval, rounded in the latter three species, oval to rounded in D. amethystoglossum; heterogeneous in D. chrysotoxum, D. griffithianum, and weakly so in D. lindleyi, palisade 2–5 cells wide, cells somewhat polygonal to oval, spongy mesophyll 4–8 cells wide, cells oval to rounded, periclinal in D. chrysotoxum and D. griffithianum, somewhat anticlinal in D. lindleyi, intercellular spaces small.

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VASCULAR BUNDLES: sclerenchyma well-developed at both xylem and phloem poles, but better developed at phloem pole in D. chrysotoxum. CRYSTALS: styloid and prismatic crystals frequent in mesophyll cells of D. griffithianum and D. palpebrae, rhomboids also occur in D. palpebrae.

Stem. CUTICLE: thick in D. chrysotoxum and D. griffithianum, moderately thick in D. lindleyi. EPIDERMIS: cells rectangular, somewhat thick-walled, and mostly periclinal in D. chrysotoxum; cells rectangular, walls very thick, laminated, conspicuously anticlinal in D. griffithianum; cells square to hexagonal and thin-walled in D. lindleyi. GROUND TISSUE: outer region consists of 2 layers of somewhat thick-walled polygonal parenchyma cells in D. chrysotoxum, 3 layers of thick-walled parenchyma cells in D. griffithianum, and 1 or 2 layers of thin-walled parenchyma cells in D. lindleyi. Waterstorage cells with pleated outlines in D. chrysotoxum and D. griffithianum. Cruciate starch grains occur in assimilatory cells in D. chrysotoxum and D. griffithianum. CRYSTALS: raphide bundles in rounded, thin-walled parenchyma cells of ground tissue in D. griffithianum and D. lindleyi. Root. VELAMEN: 4–8- and 12–14-layered, cells somewhat anticlinal but conspicuously anticlinally oriented in D. densiflorum and D. thyrsiflorum, with fine, helical, anastomosing thickening bands; outermost layer cells small, square to rectangular, mostly periclinal, either anticlinal or periclinal in D. densiflorum. EXODERMIS: walls of dead cells s-thickened somewhat thicker on outer walls in D. amethystoglossum and D. lindleyi; longitudinal walls of dead cells in D. densiflorum with small oval-bordered pits. CORTEX: 5–10 cells wide; a few scattered cells dead, empty, irregularly shaped, walls conspicuously birefringent in D. chrysotoxum, D. densiflorum, and D. griffithianum; cruciate starch grains in some cortical cells in D. densiflorum and D. griffithianum. ENDODERMIS: cells anticlinal except more or less isodiametric in D. chrysotoxum and D. thyrsiflorum; walls laminated in D. densiflorum. VASCULAR CYLINDER: 8-, 10-, 14-, 15-, or 16-arch. PITH: sclerenchymatous in D. griffithianum, D. lindleyi, and D. thyrsiflorum; parenchymatous in D. amethystoglossum, D. chrysotoxum, and D. densiflorum. CRYSTALS: raphide bundles in unmodified outer cortical cells. Section Dendrobium Species examined. D. albosanguineum, D. aphyllum, D. capillipes, D. chrysanthum, D. dixanthum, D. falconeri, D. fimbriatum, D. findlayanum, D. loddigesii, D. moschatum, D. nobile, D. parishii, D. pendulum, D. primulinum, D. pulchellum, D. senile, D. signatum, D. tortile. Leaf surface. HAIRS: typically bicellular, solitary, but paired or solitary in D. pendulum; mostly tricellular, 350 µm to 1175 µm long in D. senile. Leaf (T.S.). CUTICLE: thin, moderately thick in D. pendulum, smooth, but finely irregular in D. pendulum and over some abaxial cells in D. pulchellum, D. signatum, and D. tortile. EPIDERMIS: cells conspicuously anticlinal in D. pendulum; thin-walled. STOMATA: outer ledges medium to rather large. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 6–12-layered, cells somewhat polygonal to oval to rounded; water-storage cells in mesophyll of D. loddigesii thin-walled with pleated outlines; cruciate starch grains in mesophyll cells of D. aphyllum. VASCULAR BUNDLES: in one row, staggered in D. parishii and D. primulinum, somewhat staggered in D. aphyllum, D. pulchellum, and D. signatum; sclerenchyma equally well-developed at

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both phloem and xylem poles of midvein and lateral bundles in D. albosanguineum, D. capillipes, D. chrysanthum, D. dixanthum, D. fimbriatum, D. findlayanum, D. loddigesii, D. moschatum, D. nobile, D. parishii, D. pulchellum, and D. tortile; well-developed at both phloem and xylem poles of midvein, but occasionally better developed at xylem poles of lateral vascular bundles in D. aphyllum and D. primulinum; moderately welldeveloped over phloem pole of midvein and at both xylem and phloem poles of larger lateral bundles, but attenuated at phloem poles only of smaller lateral bundles in D. pendulum and D. signatum; very thinly developed and obscure at xylem and phloem poles of midvein and larger lateral bundles and absent from smaller lateral bundles of D. senile. Stegmata lacking in D. senile. Stem. CUTICLE: moderately thick in D. loddigesii, moderately thick to thick in D. falconeri and D. signatum, thick in D. dixanthum and D. tortile. EPIDERMIS: cells thick-walled in D. dixanthum, D. falconeri, and D. tortile, walls laminated in D. dixanthum, somewhat thinwalled in D. loddigesii, thin-walled in D. signatum. GROUND TISSUE: outer region consists of 3–5 layers of somewhat thick-walled polygonal parenchyma cells in D. dixanthum; 1 layer of very thick-walled laminated parenchyma cells in turn subtended by 2–4 layers of somewhat thick-walled polygonal parenchyma cells in D. falconeri; 1 or 2 layers of somewhat thick-walled polygonal parenchyma cells in D. loddigesii and D. tortile. In D. signatum cells of the outer region are not morphologically distinct from other ground tissue cells. Water-storage cell outlines pleated in D. dixanthum and D. tortile, unpleated in D. falconeri, D. loddigesii, and D. signatum. Starch grains in assimilatory cells of D. dixanthum, D. loddigesii, and D. signatum. Stegmata lacking in D. senile. CRYSTALS: raphide bundles in rounded, thin-walled parenchyma cells of ground tissue in D. dixanthum, D. signatum, and D. tortile. Root. VELAMEN: 4–11-layered; cells somewhat anticlinal in D. albosanguineum, D. aphyllum, D. chrysanthum, D. dixanthum, D. falconeri, D. findlayanum, D. loddigesii, D. parishii, D. pendulum, D. primulinum, and D. pulchellum; conspicuously anticlinal in D. fimbriatum, D. moschatum, D. nobile, and D. signatum; cells in 3 layers subtending outermost layer conspicuously anticlinal, but those of the innermost 5 or 6 layers only somewhat anticlinal in D. senile; slender helical anastomosing thickening bands present, thick in D. parishii, D. pendulum, and D. signatum; innermost layer of cells in D. aphyllum with inner tangential and inner portions of anticlinal walls V-thickened; outermost layer cells periclinally oriented in D. albosanguineum, D. aphyllum, D. chrysanthum, D. falconeri, D. fimbriatum, and D. loddigesii; outermost layer cells anticlinal or periclinal in D. dixanthum, D. moschatum, D. parishii, D. pulchellum, and D. senile; outermost layer cells as large as or larger than subtending cells, square, and somewhat periclinal in D. findlayanum; outermost layer cells smaller or larger than subtending cells, and mostly anticlinal in D. nobile; outermost layer cells usually larger than subtending cells, and mostly conspicuously anticlinal in D. pendulum and conspicuously anticlinal in D. pendulum and D. signatum; outermost layer cells about equal in size to subtending cells, square, and only slightly periclinal or anticlinal in D. primulinum. EXODERMIS: walls of dead cells s-thickened in most species; laminated in D. aphyllum, D. primulinum, and D. signatum; walls of dead cells s-thickened or <-thickened, outer wall much less thickened and unlaminated in D. dixanthum; walls of dead cells s-thickened or >-thickened, then much less thickened on inner wall and outer and anticlinal walls laminated in D. senile; walls of dead cells <-thickened and unlaminated in D. albosanguineum; longitudinal walls of dead cells with oval-bordered pits in D. aphyllum, D. findlayanum, D. loddigesii, D. moschatum, D. nobile, D. primulinum, D. pulchellum, and D.

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senile. CORTEX: 4–8 cells wide; cells rounded; innermost layer of cells small, periclinal; a few scattered cells larger, irregularly shaped, walls conspicuously birefringent in D. aphyllum, D. chrysanthum, D. nobile, D. primulinum, D. pulchellum, D. senile, and D. signatum; walls in D. senile with birefringent anastomosing thickening bands; cruciate starch grains present in some cells of D. dixanthum and D. signatum. ENDODERMIS: cells more or less isodiametric, but periclinal in D. dixanthum, D. fimbriatum, D. loddigesii, D. moschatum, and D. pulchellum and anticlinal in D. nobile; cell walls laminated only in D. aphyllum and D. senile. VASCULAR CYLINDER: 6-arch in D. loddigesii to 24-arch in D. moschatum, phloem segments verging on parenchyma internally in D. fimbriatum. PITH: sclerenchymatous in D. albosanguineum, D. chrysanthum, D. dixanthum, D. falconeri, D. loddigesii, D. parishii, and D. pendulum; parenchymatous in D. findlayanum, D. moschatum, D. nobile, and D. primulinum; cells somewhat thick-walled in D. aphyllum, D. pulchellum, D. senile, and D. signatum. Cruciate starch grains in some cells of D. albosanguineum and D. fimbriatum. CRYSTALS: raphide bundles in unmodified outer cortical cells in all species and in elongate saccate, thin-walled idioblasts among internal cortical cells of D. chrysanthum. Section Platycaulon Species examined. D. lamellatum, D. platygastrum. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: smooth. EPIDERMIS: cells thin-walled. STOMATA: outer ledges medium to rather large. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 5–9-layered. VASCULAR BUNDLES: sclerenchyma welldeveloped over phloem poles of midvein and lateral bundles, moderately developed over xylem pole of midvein and largest vascular bundles, less well-developed over xylem poles of smaller lateral bundles. Stem. CUTICLE: somewhat thin to moderately thick. EPIDERMIS: cells somewhat anticlinally oriented, walls very thick, laminated. GROUND TISSUE: outer region consists of 1 or 2 layers of somewhat thick-walled polygonal parenchyma cells in D. lamellatum and 3 layers in D. platygastrum. Water-storage cell outlines somewhat pleated. Root. VELAMEN: 4–8-layered; cells polygonal to irregular in D. lamellatum, with fine, helical, anastomosing thickening bands almost appearing scalariform in D. platygastrum; cells of outermost layer same size as or only somewhat smaller than subtending cells, mostly anticlinal, some periclinal in D. platygastrum; some cells domeshaped; walls of innermost velamen cells with inconspicuous V-thickenings in D. lamellatum. EXODERMIS: walls of dead cells s-thickened, somewhat thicker on outer walls in D. platygastrum, unlaminated. CORTEX: 6 or 7 cells wide; cruciate starch grains present in D. platygastrum. ENDODERMIS: cells more or less isodiametric in D.lamellatum, anticlinal in D. platygastrum. VASCULAR CYLINDER: 10- or 12-arch. PITH: sclerenchymatous in D. lamellatum, parenchymatous in D. platygastrum. CRYSTALS: raphide bundles in unmodified outer cortical cells. Section Pedilonum Species examined. D. bracteosum, D. bullenianum, D. secundum, D. smillieae.

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M. W. MORRIS ET AL. HAIRS:

bicellular, many unicellular in D. bracteosum.

Leaf (T.S). CUTICLE: thin. EPIDERMIS: cells thin-walled, flattened in D. secundum; adaxial anticlinal walls of D. bracteosum especially sinuous; abaxial anticlinal walls of D. bracteosum and adaxial anticlinal walls of D. bullenianum somewhat sinuous. STOMATA: slightly raised in D. bracteosum and D. secundum; outer ledges medium to rather large. HYPODERMIS: absent in D. bracteosum, D. bullenianum, and D. secundum; present ad- and abaxially in D. smillieae as 1 layer of somewhat large polygonal to oval thin-walled cells seemingly without chloroplasts. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 8–14 cells wide. VASCULAR BUNDLES: midvein of D. smillieae a trinary complex with one larger central bundle and two smaller lateral bundles, the phloem poles of all three bundles overlain by one continuous sclerenchymatous hippocrepiform layer of very thick-walled cells; xylem poles overlain by one continuous mass of less thick-walled sclerenchyma cells. Stem. CUTICLE: thick, thin in D. smillieae. EPIDERMIS: cell walls somewhat thickened in D. bracteosum, very thick and laminated in D. secundum and D. smillieae. GROUND TISSUE: outer region consists of 1 or 2 layers of somewhat thick-walled parenchyma cells in D. bracteosum and D. smillieae; 4–6 layers of somewhat thick-walled parenchyma cells in D. secundum; 2–6 layers of thin-walled, polygonal to rounded parenchyma cells with chloroplasts but without starch grains in D. smillieae. Waterstorage cell outlines pleated. VASCULAR BUNDLES: thin-walled sclerenchyma cells at xylem poles of larger bundles in D. secundum. Stegmata associated with xylem pole sclerenchyma of the larger internal bundles of D. secundum. Root. VELAMEN: 3–8-layered, cells mostly conspicuously anticlinal but only inner 3 layers in D. bracteosum; only somewhat anticlinal in D. smillieae, with fine helical anastomosing thickening bands, those in outer two cell layers conspicuously thicker and walls of innermost cells V- to <-thickened in D. secundum; cells of outermost layer smaller, rectangular to square, mostly periclinal in D. bracteosum and D. bullenianum; outermost layer of cells small, square, and anticlinal or periclinal in D. secundum and D. smillieae. EXODERMIS: walls of dead cells s-thickened, thickest on outer tangential walls in D. bracteosum, D. secundum, and D. smillieae, approaching the >-thickened state in D. secundum; longitudinal walls with oval-bordered pits in D. secundum and D. smillieae. CORTEX: 4–6, 8 or 9 cells wide; a few cells of the innermost layer dead, empty, with conspicuously birefringent walls. ENDODERMIS: cells anticlinal in D. smillieae. VASCULAR CYLINDER: 7-, 8-, 13-, or 16-arch. PITH: sclerenchymatous in D. bullenianum and D. secundum, parenchymatous in D. bracteosum and D. smillieae. CRYSTALS: raphide bundles in unmodified outer cortical cells in D. bracteosum, D. secundum, and D. smillieae.

Section Brachyanthe Species examined. D. alterum, D. hercoglossum. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S). CUTICLE: thin, smooth on both surfaces of D. alterum and adaxially in D. hercoglossum; thin, rugulose, abaxially in D. hercoglossum. EPIDERMIS: cells thin-walled; anticlinal walls of adaxial epidermises somewhat sinuous. STOMATA: outer ledges

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small to medium, inner ledges minute. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 7–9 cells wide, cells polygonal to oval to rounded in D. alterum, all cells rounded in D. hercoglossum. VASCULAR BUNDLES: sclerenchyma welldeveloped at both phloem and xylem poles of midvein and lateral bundles in D. hercoglossum, only well-developed at phloem pole of midvein and only a small amount of sclerenchyma above xylem of other major bundles in D. alterum. Stem. CUTICLE: moderately thick in D. alterum, thick in D. hercoglossum. EPIDERMIS: cells tangentially flattened and thin-walled in D. alterum, cell walls somewhat thickened in D. hercoglossum. GROUND TISSUE: outer region consists of 1 layer of small, polygonal, thin-walled parenchyma cells in D. alterum; 2 or 3 layers of somewhat thick-walled parenchyma cells in D. hercoglossum. Water-storage cell outlines pleated in D. hercoglossum, unpleated in D. alterum; cruciate starch grains in assimilatory cells of D. hercoglossum. Root. VELAMEN: 5–7-layered, cells polygonal to irregular to almost rounded in D. hercoglossum, mostly somewhat to moderately anticlinal with fine helical anastomosing thickening bands; outermost layer cells only slightly smaller than subtending cells, these polygonal, periclinal or anticlinal. EXODERMIS: walls of dead cells s-thickened, <-thickened in D. hercoglossum, unlaminated. CORTEX: 5 or 6 cells wide; cells mostly somewhat polygonal in D. alterum, mostly rounded in D. hercoglossum; cells of outermost two and innermost single layer in D. alterum smaller than other cortical cells and distinctly polygonal; cells of outermost 1 or 2 layers in D. hercoglossum small, more or less polygonal, cells of innermost 1 or 2 layers of cells small, frequently tangentially flattened. ENDODERMIS: cells more or less isodiametric in D. alterum, anticlinal in D. hercoglossum. VASCULAR CYLINDER: 9- or 11-arch. PITH: sclerenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells in D. alterum. Section Stachyobium Species examined. D. compactum, D. delacourii. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: thin. EPIDERMIS: adaxial cells conspicuously larger than abaxial in D. compactum and anticlinal; cells thin-walled. STOMATA: outer ledges medium to rather large. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 7- or 8-layered, cells rounded to irregular. VASCULAR BUNDLES: sclerenchyma developed mostly at phloem poles of midvein and of lateral bundles in D. delacourii, weakly developed at both phloem and xylem poles of all bundles in D. compactum. Stem. CUTICLE: moderately thick in D. compactum, moderately thick to thick in D. delacourii. EPIDERMIS: cells periclinal, slightly thick-walled. GROUND TISSUE: outer region consists of 2 or 3 layers of somewhat thick-walled polygonal parenchyma cells in D. delacourii. Water-storage cells with pleated walls. Root. VELAMEN: 4- or 5-layered, cells polygonal in D. compactum, polygonal to rounded in D. delacourii, somewhat anticlinal, with very fine, helical, anastomosing thickening bands; outermost layer of cells square. EXODERMIS: walls of dead cells s- to

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<-thickened in D. compactum, mostly <-thickened in D. delacourii. CORTEX: 5 or 6 cells wide. ENDODERMIS: cells periclinal. VASCULAR CYLINDER: 5- or 6-arch. PITH: sclerenchymatous, cell walls laminated in D. delacourii. CRYSTALS: raphide bundles in unmodified outer cortical cells. Section Phalaenanthe Species examined. D. bigibbum, D. williamsianum. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: thin. EPIDERMIS: cells thin-walled. STOMATA: outer ledges medium to rather large. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 6- or 7-layered in D. williamsianum, 13- or 14-layered in D. bigibbum. VASCULAR BUNDLES: sclerenchyma mostly developed at phloem pole, cells much thinner-walled at xylem pole in D. bigibbum; well-developed at both xylem and phloem poles in D. williamsianum. CRYSTALS: druses in widely, scattered mesophyll cells in D. bigibbum. Stem. CUTICLE: moderately thick. EPIDERMIS: cells rectangular to hexagonal, periclinal, slightly thick-walled. GROUND TISSUE: outer region consists of 1–3 layers of somewhat thick-walled polygonal parenchyma cells. Water-storage cells with slightly pleated walls. Root. VELAMEN: 5- or 6-layered, slightly anticlinal, anastomosing thickening bands fine, obscure; cells of outermost layer same size as or only somewhat smaller than subtending cells, polygonal, mostly slightly anticlinal. EXODERMIS: walls of dead cells <-thickened, laminated. CORTEX: data unavailable. ENDODERMIS: cells more or less isodiametric to somewhat periclinal. Data on vascular cylinder unavailable. Section Eleutheroglossum Species examined. D. fellowsii. Leaf surface. HAIRS: bicellular, some unicellular. EPIDERMIS: cells polygonal. STOMATA: abaxial. Leaf (T.S.). Leaves fleshy. CUTICLE: moderately thick adaxially, thin abaxially, smooth both surfaces. EPIDERMIS: cells somewhat periclinal, thin-walled. STOMATA: superficial to slightly raised, inner ledges minute. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 16–20-layered, cells rounded, circular. VASCULAR BUNDLES: in one row; sclerenchyma best developed at phloem pole, but also at xylem poles of some larger lateral bundles. CRYSTALS: Druses in some mesophyll cells near the midvein. Stem. CUTICLE: moderately thick to thick. EPIDERMIS: cells mostly periclinal, outer wall very thick and laminated, other walls thin. GROUND TISSUE: outer region consists of 2 or 3 layers of thick-walled parenchyma cells. Water-storage cell outlines pleated. Root. VELAMEN: 7- or 8- or 10–12-layered, anastomosing thickening bands obscure, fine, helical; outermost layer of cells square. EXODERMIS: walls of dead cells

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s-thickened. CORTEX: 6–9 cells wide, cells rounded. ENDODERMIS: cells more or less isodiametric. VASCULAR CYLINDER: 11- or 15-arch. PITH: sclerenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells.

Section Spatulata Species examined. D. antennatum, D. canaliculatum, D. taurinum. Leaf surface.

HAIRS:

bicellular, some unicellular in D. antennatum.

Leaf (T.S.). CUTICLE: thin, smooth adaxially, rugulose abaxially in D. antennatum and on both surfaces of D. canaliculatum; moderately thick, smooth adaxially, thin to moderately thick and irregular abaxially in D. taurinum. EPIDERMIS: cells square to hexagonal, somewhat anticlinal in D. canaliculatum, anticlinal inner walls sinuous in D. antennatum; cells thin-walled in D. antennatum and D. taurinum, somewhat thick-walled in D. canaliculatum, outer walls on both surfaces in D. taurinum somewhat thick. STOMATA: bifacial in D. canaliculatum, abaxial in D. antennatum and D. taurinum; outer ledges medium to rather large, inner ledges conspicuous in D. canaliculatum. HYPODERMIS: weakly defined adaxially and abaxially in D. taurinum and D. canaliculatum, 1-layered, cells thin-walled, somewhat thicker than subtending mesophyll cells, somewhat polygonal to rounded, anticlinal or periclinal adaxially, rounded only abaxially. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous in D. antennatum and D. canaliculatum; weakly heterogeneous in D. taurinum, palisade 3 or 4 cells wide, only somewhat anticlinal, spongy mesophyll 8–12 cells wide. Stem. CUTICLE: thin to moderately, thick. EPIDERMIS: cells somewhat thick-walled, very thick-walled and laminated in D. canaliculatum. GROUND TISSUE: outer region consists of 2 or 3 and 3 or 4 layers of thick-walled polygonal parenchyma cells. Water-storage cell outlines unpleated. Root. VELAMEN: 6–12-layered, mostly conspicuously anticlinal in D. antennatum, only somewhat anticlinal in D. taurinum, with fine, helical, anastomosing thickening bands; outermost layer of cells small, square, periclinal or anticlinal. EXODERMIS: dead cell walls s-thickened. CORTEX: 6–9 cells wide; cells somewhat polygonal in D. antennatum, rounded and somewhat anticlinal in D. taurinum, rounded to irregular in D. canaliculatum, scattered cells in D. taurinum large, empty, dead, and somewhat rounded with conspicuously birefringent walls; fungal pelotons occur in certain cortical cells. ENDODERMIS: cells more or less isodiametric in D. antennatum and D. canaliculatum, anticlinal in D. taurinum. VASCULAR CYLINDER: 18- or 21-arch. PITH: parenchymatous, cells somewhat thick-walled in D. taurinum. CRYSTALS: raphide bundles in unmodified outer cortical cells and in thin-walled, elongate, saccate idioblasts in the middle region of the cortex in D. taurinum.

Section Formosae Species examined. D. cruentum, D. dearei, D. formosum, D. sanderae, D. schuetzei, D. virgineum. Leaf surface.

HAIRS:

bicellular, solitary or paired (Fig. 13).

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Leaf (T.S.). CUTICLE: thin in all species, except D. schuetzei where it is moderately thick; smooth on both surfaces, except abaxially it is irregular in D. schuetzei and finely irregular over some abaxial cells in D. sanderae. EPIDERMIS: cells thin-walled; somewhat anticlinal in D. schuetzei; anticlinal walls of adaxial cells sinuous in D. cruentum and D. formosum. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 8–12-layered, cells somewhat polygonal to oval to rounded. VASCULAR BUNDLES: sclerenchyma well-developed at both xylem and phloem poles of midvein and most lateral bundles, except in D. cruentum sclerenchyma of lateral bundles mostly at phloem pole. Stem. CUTICLE: moderately thick in D. formosum, moderately thick to thick in D. dearei. EPIDERMIS: cells mostly periclinal, somewhat thick-walled in D. formosum, thick-walled in D. dearei. GROUND TISSUE: outer region consists of 2 or 3 layers of somewhat thickwalled polygonal parenchyma cells. Water-storage cell outlines pleated. Root. VELAMEN: 4–12- and 14–17-layered, cells somewhat anticlinal to conspicuously anticlinal in D. sanderae, with fine, helical, anastomosing thickening bands; outermost layer of cells mostly periclinal in D. cruentum, D. dearei, and D. sanderae; somewhat anticlinal in D. formosum, D. schuetzei, and D. virgineum. EXODERMIS: walls of dead cells s-thickened, walls of some dead cells in D. cruentum and D. virgineum >-thickened, unlaminated except in D. virgineum; longitudinal walls of dead cells with ovalbordered pits in D. dearei, D. sanderae, and D. schuetzei. CORTEX: 5–9 cells wide; some living cortical cells with birefringent anastomosing thickening bands in D. sanderae and D. schuetzei; scattered cortical cells dead, empty, walls conspicuously birefringent in D. sanderae and D. schuetzei. ENDODERMIS: cells more or less isodiametric in D. cruentum, D. dearei, and D. virgineum, anticlinal in D. sanderae and D. schuetzei, periclinal in D. formosum. VASCULAR CYLINDER: 8-, 10-, 11-, 14-, 15-, or 18-arch. PITH: sclerenchymatous in D. cruentum, D. dearei, D. sanderae, and D. schuetzei; parenchymatous in D. formosum and D. virgineum. CRYSTALS: raphide bundles in unmodified outer cortical cells. Section Rhopalanthe Species examined. D. clavator, D. crumenatum. Leaf surface. HAIRS: bicellular, mostly abaxial in D. clavator. rectangular in D. clavator.

EPIDERMIS:

cells largely

Leaf (T.S.). Leaves conduplicate to centric. CUTICLE: thin on both surfaces of D. clavator; moderately thick adaxially, thin abaxially in D. crumenatum. EPIDERMIS: cells somewhat thick-walled, outer walls conspicuously thickest in D. clavator. STOMATA: somewhat sunken in D. clavator. HYPODERMIS: subtending the adaxial epidermis are 1 or 2 layers of rectangular, horizontally oriented, thin-walled cells; subtending the abaxial epidermis are 1 or 2 layers of somewhat oval, horizontally oriented, thinwalled cells in D. crumenatum. FIBRE BUNDLES: one row subtending abaxial hypodermis in D. crumenatum, cells uniformly thick-walled; absent in D. clavator. CHLORENCHYMA: homogeneous, leaves unifacial, c. 22 cells wide in D. clavator, 14- or 15-layered in D. crumenatum, cells mostly rounded, and larger toward the centre of the T.S. in D. clavator; cells polygonal to oval in D. crumenatum. VASCULAR BUNDLES: in one row concentric with leaf outline in D. clavator; in three horizontal series on either side of

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the midvein in D. crumenatum, bundles of adaxial series are largest. Sclerenchyma well-developed at phloem pole of each bundle in D. clavator; in D. crumenatum, more well-developed at xylem pole of adaxial and middle row of bundles with some occurring at phloem pole of middle row of bundles, better-developed at phloem pole of abaxial row of bundles and nearly equally well-developed at both xylem and phloem poles of midvein. Stem. CUTICLE: moderately thick. EPIDERMIS: outer cell walls conspicuously thickened; all walls laminated. GROUND TISSUE: outer region consists of 1 or 2 layers of somewhat thick-walled polygonal parenchyma cells. Water-storage cells with thin, strongly birefringent walls, outlines pleated in D. clavator. CRYSTALS: raphide bundles in ground tissue cells of D. clavator. Root. VELAMEN: 4–7-layered, cells anticlinal with very fine helical anastomosing thickening bands that appear scalariform in T.S.; outermost layer of cells periclinal. EXODERMIS: walls of dead cells s-thickened, unlaminated. CORTEX: 5–8 cells wide. VASCULAR CYLINDER: 9-arch in D. clavator, 21-arch in D. crumenatum. PITH: parenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells.

Section Aporum Species examined. D. acerosum, D. acinaciforme, D. anceps, D. leonis. Leaf surface. Leaves unifacial, bilaterally symmetrical internally. The entire exposed leaf surface is abaxial. HAIRS: unicellular or bicellular. Leaf (T.S.). CUTICLE: thin, smooth in D. acerosum and D. acinaciforme; moderately thick, smooth, conspicuously intermittently domed in D. anceps and flat in D. leonis. EPIDERMIS: cells mostly periclinal in D. acerosum and D. anceps; somewhat thick-walled in D. acinaciforme. STOMATA: superficial to slightly raised; thick-walled parenchyma cells laterally flank each substomatal chamber in D. leonis; outer ledges medium to rather large. HYPODERMIS: abaxial in all species; 1-layered in D. anceps, 2 in D. acerosum, 2 or 3 in D. acinaciforme and D. leonis; cells small, periclinal. FIBRE BUNDLES: abaxial, subtending the hypodermis in all species, 1 series in D. acerosum and D. anceps, cells uniformly thick-walled in D. acerosum, outer cells thicker-walled than subtending cells in D. anceps; 2 alternating, somewhat staggered series of bundles in D. acinaciforme (Fig. 5) and D. leonis; inner series bundles smaller, cells uniformly thick-walled, outer series bundles larger and outer cells of each bundle thicker-walled than subtending cells in D. acinaciforme; inner series bundles larger and outer cells of each bundle thicker-walled than subtending cells, outer series bundles with cells uniformly thickwalled, inner series fibre bundles directly subtending substomatal chambers in D. leonis. Stegmata occur regularly along outer margins of fibre bundles in all four species and are sometimes present at the inner margins of fibre bundles in D. acerosum; stegmata are not associated with outer series of smaller fibre bundles in D. leonis but occur in both series in D. acinaciforme. CHLORENCHYMA: homogeneous, 32 cells wide across middle in D. acerosum, 49 cells wide across middle in D. acinaciforme, 27 cells wide across middle in D. anceps, 30 cells wide across middle in D. leonis; cells oval, anticlinal toward periphery to rounded to oval, periclinal toward middle, to irregular. Periclinal water-storage cells with pleated walls present toward middle of

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leaf in D. acerosum, D. acinaciforme, and D. leonis. Water-storage cells with pleated walls scattered throughout mesophyll but concentrated toward middle of leaf in D. anceps. VASCULAR BUNDLES: phloem poles facing epidermis, xylem poles facing foliar midline; bundle series parallel midline on either side; putative midvein wider than other bundles situated at one terminus of foliar midline; irregularly aligned in three series in D. acerosum and D. acinaciforme, in one series in D. anceps and D. leonis. Sclerenchyma usually conspicuous but not well-developed at phloem poles of midvein and largest lateral bundles, poorly developed at xylem poles of midvein and largest lateral bundles and at phloem poles of smaller bundles, absent from xylem poles of smaller bundles. Bundle sheath cells forming continuous or nearly continuous series. Stegmata present in D. anceps, D. acinaciforme, and D. acerosum; absent from D. leonis. Stem. CUTICLE: moderately thick to thick in D. acerosum and D. anceps, thick in D. acinaciforme, intermittently undulating in D. anceps. EPIDERMIS: cells thick-walled in D. acerosum and D. acinaciforme, thin-walled in D. anceps. GROUND TISSUE: outer region consists of 2–4 layers of thick-walled polygonal parenchyma cells in D. acerosum, 3 or 4 layers in D. acinaciforme, and 1 or 2 layers in D. anceps. Water-storage cell outlines unpleated. Root. VELAMEN: 4–6-layered, fine helical anastomosing thickening bands; outermost layer of cells slightly rectangular to square to polygonal, periclinal, either anticlinal or periclinal in D. anceps. EXODERMIS: walls of dead cells s-thickened, unlaminated. CORTEX: 4–7 cells wide. ENDODERMIS: cells anticlinal. VASCULAR CYLINDER: 6-, 8-, or 9-arch. PITH: sclerenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells. Section Grastidium Species examined. D. salaccense. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: thin. EPIDERMIS: cells thin-walled, anticlinal walls of both adaxial and abaxial epidermises occasionally sinuous. STOMATA: outer ledges medium. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 6–8 cells wide, cells mostly rounded to oval, intercellular spaces minute and infrequent. VASCULAR BUNDLES: Bundle sheath cells thin-walled, forming discontinuous layers. Stem. CUTICLE: moderately thick. EPIDERMIS: cells mostly pentagonal to hexagonal, somewhat thick-walled. GROUND TISSUE: outer region consists of 1–3 layers of somewhat thick-walled polygonal parenchyma cells. Inner tissue homogeneous, comprising rounded to somewhat polygonal, thin-walled living parenchyma cells; water-storage cells absent; intercellular spaces present; cruciate starch grains numerous in parenchyma cells. Root. VELAMEN: 5–8-layered, anticlinal to nearly so, fine helical anastomosing thickening bands present; cells of outermost layer periclinal. TILOSOMES: present adjacent to passage cells of exodermis (Fig. 14). EXODERMIS: walls of dead cells s-thickened, unlaminated. CORTEX: 11 or 12 or 18 cells wide; a few larger,

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irregularly shaped cells with conspicuously birefringent walls scattered among smaller cortical cells. ENDODERMIS: cells more or less isodiametric. VASCULAR CYLINDER: 27-arch. PITH: parenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells.

Section Macrocladium Species examined. D. cunninghamii. Leaf surface.

HAIRS:

bicellular rarely uni- or tricellular.

Leaf (T.S.). CUTICLE: moderately thick to thick adaxially, moderately thick abaxially. EPIDERMIS: cells somewhat anticlinal, somewhat thin-walled. STOMATA: somewhat sunken. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous (11)13- or 14-layered, cells mostly oval. VASCULAR BUNDLES: Bundle sheath cells forming nearly continuous or continuous layers. Stem. CUTICLE: thick. EPIDERMIS: cells polygonal, angles very blunt, cells appearing quite rounded, cell walls very thick, laminated. GROUND TISSUE: outer region 7–10 cells wide, cell walls very thick, laminated. Inner tissue homogeneous comprising rounded to somewhat polygonal, thick-walled parenchyma cells, walls of some laminated; water-storage cells absent; cruciate starch grains numerous in parenchyma cells. Root. VELAMEN: 4- or 5(6)-layered, cells polygonal to rectangular, periclinal, with fine helical anastomosing thickening bands; cells of outermost layer mostly rectangular, periclinal. EXODERMIS: walls of dead cells s-thickened, laminated. CORTEX: 12–14 cells wide; cells oval, anticlinal to somewhat polygonal to rounded, many cells with birefringent fine helical anastomosing thickening bands; scattered cells irregularly shaped, walls strongly birefringent. ENDODERMIS: cells more or less isodiametric. VASCULAR CYLINDER: 10- or 11-arch. PITH: parenchymatous.

Section Monanthos Species examined. D. malbrownii. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: moderately thick. EPIDERMIS: cells mostly rectangular to hexagonal, thin-walled. HYPODERMIS: absent. FIBRE BUNDLES: adaxial smaller, widely spaced, in one series, cells uniformly thick-walled; abaxial larger, evenly and more closely spaced than the former, in one series, cells uniformly thick-walled. Stegmata associated with inner (rarely) and outer margins of adaxial bundles, but only with outer margins of abaxial bundles. CHLORENCHYMA: heterogeneous; palisade seriation 1–3, cells columnar-oval to almost circular and only somewhat anticlinal; spongy seriation 6–8, cells mostly rounded, scattered cells large, irregularly shaped, walls conspicuously birefringent; intercellular spaces very few and minute. VASCULAR BUNDLES: bundle sheath cells thin-walled around midvein forming a discontinuous layer; thick-walled cells alternate with thin-walled cells around lateral bundles and

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form continuous or discontinuous sheaths. Silica bodies very large, to 30.0 µm diam. Stem. CUTICLE: thin to moderately thick. EPIDERMIS: cells polygonal mostly hexagonal. GROUND TISSUE: outer region consists of 2 or 3 layers of very thick-walled polygonal parenchyma cells subtended by 2 or 3 layers of less thick-walled polygonal parenchyma cells. Inner tissue homogeneous comprising rounded to somewhat polygonal, thin-walled parenchyma cells; water-storage cells absent. VASCULAR BUNDLES: outermost bundles closely adjacent in an irregular ring each surrounded by a sclerenchyma sheath more strongly developed on the phloem side; internal bundles scattered, each surrounded by a single layer of thick-walled parenchyma cells. Root. VELAMEN: 4-layered, cells polygonal, cells of innermost layer conspicuously anticlinal, walls V-thickened internally; cells of second layer somewhat anticlinal, cells of third layer mostly isodiametric, cells of outermost layer mostly rectangular, periclinal; fine helical anastomosing thickening bands characterize most cells. TILOSOMES: present, adjacent to passage cells of exodermis (Fig. 15). EXODERMIS: walls of dead cells >-thickened, unlaminated. CORTEX: 17–19 cells wide; scattered cells larger, empty, dead, irregularly shaped, walls strongly birefringent; cruciate starch grains in some cells. ENDODERMIS: cells more or less isodiametric. VASCULAR CYLINDER: 15-arch. PITH: parenchymatous. CRYSTALS: raphide bundles in unmodified outer cortical cells. Sections Phalaenanthe/Spatulata Species examined. D. 3 superbiens. Dendrobium 3 superbiens is a natural hybrid between D. bigibbum, section Phalaenanthe and D. discolor, section Spatulata. Leaf surface.

HAIRS:

bicellular.

Leaf (T.S.). CUTICLE: thin, smooth adaxially, finely irregular abaxially. EPIDERMIS: cells rectangular to hexagonal, mostly periclinal, thin-walled. HYPODERMIS: adaxial, 1-layered, cells small, somewhat periclinal or slightly anticlinal; very weakly defined abaxially, 1-layered, cells small, somewhat periclinal or slightly anticlinal. FIBRE BUNDLES: absent. CHLORENCHYMA: weakly heterogeneous, palisade 3–5 cells wide, cells polygonal to oval, thin-walled, and mostly only somewhat anticlinal; spongy mesophyll 8–9 cells wide, cells somewhat polygonal to rounded, intercellular spaces confined to spongy mesophyll few, minute, irregular. VASCULAR BUNDLES: little sclerenchyma developed at xylem poles of smaller bundles. Stem. CUTICLE: thick. EPIDERMIS: cells rectangular to hexagonal, walls very thick, laminated. GROUND TISSUE: outer region consists of 3 or 4 layers of thick-walled polygonal parenchyma cells. Water-storage cells with pleated outlines. Root. VELAMEN: 9- or 10-layered, cells polygonal to irregular, mostly only somewhat anticlinal, with fine, helical, anastomosing thickening bands; outermost layer of cells Figures 13–16. Fig. 13. Dendrobium cruentum. Abaxial foliar epidermis scraping showing paired hairs. × 245. Figs 14, 15. Transverse sections exodermis with passage cells (p) subjacent to tilosomes (t) in adjoining velamen cells. Fig. 14. D. salaccense. ×3225. Fig. 15. D. malbrownii. × 1820. Fig. 16. Pseuderia platyphylla. Abaxial foliar epidermis scraping showing tetracytic and cyclocytic stomatal apparatuses. × 510. Scale bars = 10 µm.

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small, square, periclinal or anticlinal. EXODERMIS: walls of dead cells s-thickened. CORTEX: 6 or 7 cells wide; cells rounded, scattered cells dead, empty, rounded to somewhat polygonal, walls conspicuously birefringent. ENDODERMIS: cells anticlinal. VASCULAR CYLINDER: 10-arch. PITH: parenchymatous. CRYSTALS: raphide bundles in both unmodified cells and thin-walled, elongate, saccate cells of the outer cortex.

Anatomy of Pseuderia Species examined. P. foliosa, P. micronesiaca, P. platyphylla, P. ramosa, P. similis, P. smithiana. Leaf surface. HAIRS: uniseriate, relatively few, bicellular, occasionally tricellular in P. foliosa and P. smithiana, solitary, glandular, sunken, on both surfaces. EPIDERMIS: cells polygonal, anticlinal walls more or less straight-sided on both surfaces, curvilinear in many cells, the angles then rounded among cells. STOMATA: abaxial, basically tetracytic, frequently cyclocytic (Fig. 16), and rarely anisocytic in P. platyphylla, P. foliosa, P. micronesiaca, and P. ramosa; ranges of means for guard cell pairs: 30–36 µm long, 24–30 µm wide (Table 3). Leaf (T.S.). Leaves conduplicate. CUTICLE: thin, smooth. EPIDERMIS: cells mostly square to rectangular to pentagonal, thin-walled; anticlinal walls of cells of both adaxial and abaxial epidermises frequently sinuous. STOMATA: superficial, substomatal chambers large and trapezoidal, outer ledges medium, inner ledges minute. HYPODERMIS: absent. FIBRE BUNDLES: absent. CHLORENCHYMA: homogeneous, 5–12 cells wide, cells of uppermost single row polygonal, other cells mostly oval but rounded in a few abaxial cells, thin-walled; intercellular spaces few, irregular, and concentrated toward abaxial epidermis. Water-storage cells absent (Table 5). VASCULAR BUNDLES: collateral, in one row. Sclerenchyma very well-developed at both xylem and phloem poles of all larger bundles, less well-developed in smaller bundles. Bundle sheath cells thin-walled, forming a continuous series around bundles. Stegmata absent. CRYSTALS: raphide bundles in thin-walled, elongated saccate cells of mesophyll. Stem. CUTICLE: thin in P. micronesiaca, thin to moderately thick in P. ramosa, moderately thick in P. foliosa, moderately thick to thick in P. platyphylla, P. similis, and P. smithiana, smooth. EPIDERMIS: cells small, rounded to somewhat polygonal, square to hexagonal; walls very thick, laminated in P. foliosa, slightly thick-walled in P. micronesiaca and P. ramosa, thin-walled in P. platyphylla, P. similis, and P. smithiana. GROUND TISSUE: zonate, zone 1 subtends the epidermis, zone 2 subtends zone 1 exterior to the ring of vascular bundles, and zone 3 represents the central core. Zone 1 is 1–3 cells wide; zone 2 is 3 or 4, 3–6, 7–9, 3–5, 6–8, and 8–12 cells wide in P. foliosa, P. micronesiaca, P. platyphylla (Fig. 17), P. ramosa, P. similis, and P. smithiana, respectively. Cell wall thickness decreases from thick and very thick in zone 1 cells to thin in core zone cells; thick and very thick cell walls are laminated. Cell diameters decrease from narrow in zone 1 to wide in cells of the central core, these being up to four times the diameter of zone 1 cells. Cells are oval to polygonal and periclinal throughout; intercellular spaces are absent or minute among zone 1 cells and prominent among cells of the core. Most cells appear to be living and contain cruciate starch grains. There are scattered gelatinous fibres with strongly birefringent

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inner cell wall layers and rather small lumina; gelatinous fibres are absent in P. similis. Water-storage cells absent. VASCULAR BUNDLES: collateral, and with associated sclerenchyma forming a ring internal to zone 2 cells of ground tissue and scattered in ground tissue core (Fig. 17); bundle sclerenchyma mostly associated with phloem pole, some present at xylem pole, many cells very thick-walled, laminated. Stegmata absent. CRYSTALS: raphide bundles in rounded to oval, thin-walled idioblasts of ground tissue. Root. VELAMEN: cells square, comprising 2 or 3 layers (Table 8), tangential walls thickest, thickening bands absent; outermost cells frequently modified into unicellular hairs. TILOSOMES: absent. EXODERMIS: cell walls thin, outer and anticlinal walls somewhat thicker than inner walls (Fig. 18, Table 8); thickenings on longitudinal walls of dead cells absent; passage cells occur at irregular intervals. CORTEX: 8 or 9 cells wide in P. smithiana (Fig. 18), 9–11 cells wide in P. platyphylla (Table 8); cells parenchymatous, mostly polygonal to irregular, slightly thick-walled, outermost single layer of cells somewhat smaller than subtending cells, innermost 1 or 2 layers of cells small, frequently tangentially flattened, often thick-walled; raphidecontaining cells scattered, wider than surrounding cells; intercellular spaces present.

Figures 17, 18. Fig. 17. Pseuderia platyphylla. Transverse section stem; ground tissue lacks water-storage cells. Outermost tissue band is the leaf sheath (ls); zone 1 cells subtend the epidermis, zone 2 cells subtend zone 1 cells external to the sclerenchyma (s) of the ring of vascular bundles, and zone 3 cells represent the central cauline core in which most of the vascular bundles are scattered. × 105. Fig. 18. P. smithiana. Transverse section root with 2-layered velamen (v) subtended by exodermis (e) of thin-walled almost isodiametric cells. Cortex (c) consists of thin-walled parenchyma cells. Vascular tissues are embedded in sclerenchyma (s) and parenchymatous pith cells (pi) are thick-walled. × 235. Scale bars = 10 µm.

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uniseriate, cells strongly anticlinal, walls laminated, s-thickened opposite phloem sectors, thin-walled opposite xylem sectors. PERICYCLE: uniseriate, cell walls s- or <-thickened opposite phloem sectors, unthickened opposite xylem sectors (Table 8). VASCULAR CYLINDER: 11-arch in P. smithiana (Fig. 18), 18-arch in P. platyphylla (Table 8), vascular elements embedded in sclerenchyma with xylem and phloem segments alternating around the circumference. PITH: parenchymatous, cells thick-walled (Table 8). CRYSTALS: raphide bundles in large, polygonal to irregularly shaped cortical cells. ENDODERMIS:

DISCUSSION

A significant problem in seeking adequately to characterize the anatomy of the three genera comprising Dendrobiinae is the lack of reliable representation in the study material of some groups. In extreme instances we had only a single species to represent some sections of Dendrobium — Goniobulbon, Bolbidium, Inobulbon, Grastidium, Macrocladium, and Monanthos — and in a few cases we lacked some plant parts for study. Thus the comparisons we make below among anatomical features in different taxa must be considered with these limitations in mind. Nevertheless, we believe our anatomical observations to be valid and our generalizations of the anatomy of Cadetia, Dendrobium, and Pseuderia to be representative of the anatomical spectrum displayed in these genera. Results of this study indicate that the basic pattern of floral morphology described for Dendrobiinae by Schlechter is more constant than vegetative morphological and anatomical characteristics in many of the taxa currently included in the subtribe. The floral ‘column-foot’ is present in varying degrees in every taxonomic group except the genus Pseuderia; four ‘naked’ pollinia occur uniformly throughout the subtribe except for section Sarcopodium (the genus Epigeneium as recognized by some authors). The wide variety of vegetative morphology in Dendrobiinae is reflected in a correspondingly diverse vegetative anatomy. Sometimes morphology and anatomy correlate in diagnosing taxa; other times vegetative morphological similarities defining a taxonomic group are not supported by anatomical data. Stomata are all abaxial in Dendrobiinae, but in D. canaliculatum, section Spatulata, stomata occur on both leaf surfaces. The predominant pattern of the mature stomatal complex in most Dendrobiinae is paracytic (Fig. 3), a configuration in which there are usually only two subsidiary cells laterally flanking the guard-cell pair, one on each side. This paracytic pattern shows perigenous stomatal development (Norris H. Williams, pers. comm.) in which oblique divisions of guard-cell neighbouring cells result in either trapezoid cells or triangular cells that are capable of further nonoblique divisions, ultimately forming the subsidiary cells. Occasionally two subsidiary cells occur on each side of the guard-cell pair, with the dividing wall between the two orientated perpendicularly to the long axis of the guard-cell pair. Thus, three or four lateral subsidiary cells may be present. The guard cells are derived from division of the guard-cell mother cell after subsidiary cells are formed. Derivation of the paracytic stomatal complex outlined above for many Dendrobiinae is the same as the developmental pathway in the formation of the stomatal complex for many members of Oncidieae (Williams, 1979). Rasmussen (1987) referred to the mature stomatal complex described by Williams as paracytic. Singh (1981) reported mesoperigenous stomatal development in some species of

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Dendrobium, where one subsidiary cell is derived from the same meristemoid as the guard-cell mother cell, and the other subsidiary cells result from divisions of neighbouring cells. Because our investigation did not include developmental studies, we could not test the validity of Singh’s findings. As far as we know, his report of mesoperigenous development has not been verified. But, in light of the very thorough study conducted by Williams (1979), and because of our discussions with him about stomata, we are satisfied to attribute perigenous stomatal development to Dendrobiinae. In sections Bolbidium and Rhizobium the paracytic condition characterizing all other taxa in Dendrobiinae, is replaced by the tetracytic configuration. In addition, stomata in these sections also show the cyclocytic organization. Some leaves in Sarcopodium have paracytic, tetracytic, and anisocytic stomatal arrangements. Pseuderia leaves have predominantly tetracytic stomatal configurations, but the cyclocytic pattern is frequent (Fig. 16) and even anisocytic stomata occur occasionally. According to Rasmussen (1987), the tetracytic configuration is “dependent on a regular epidermal pattern, in which exactly four cells of approximately equal size abut the guard cell pair.” The anisocytic pattern was occasionally observed in Pseuderia (P. foliosa, P. micronesiaca, P. ramosa), and in sections Sarcopodium (Dendrobium amplum) and Platycaulon (D. lamellatum). Rasmussen suggested the anisocytic condition, where there are three subsidiary cells, is due to an irregular epidermis in species usually exhibiting the tetracytic configuration. We found four to six subsidiary cells in Dendrobium pachyphyllum (section Bolbidium), D. lichenastrum and D. rigidum (section Rhizobium), Pseuderia platyphylla and P. ramosa; four or five subsidiary cells in D. cucumerinum, D. linguiforme, D. schoeninum, D. teretifolium, and D. wassellii (section Rhizobium), and in Pseuderia foliosa, P. micronesiaca, P. similis, and P. smithiana; and four to eight subsidiary cells in D. toressae (section Rhizobium), all of which correspond to the cyclocytic pattern. Rasmussen (1987) described the cyclocytic configuration as a ring of five or more subsidiary cells. Pridgeon & Williams (1979) hypothesized that a subsequent radial division of the four subsidiary cells in the normally tetracytic configuration would result in this condition. Water-storage cells of two kinds are present in leaves and/or stems of many taxa in Dendrobiinae, in the mesophyll and/or hypodermis and in the cauline ground tissue, i.e. cells with pleated (Fig. 11) or unpleated (Fig. 7) walls and cells with secondary wall thickenings. Secondary thickenings are represented mostly by helical bands as in both sections of Cadetia (Fig. 2), in Dendrobium section Inobulbon, and in Dendrobium toressae, section Rhizobium. Other taxa, including some species in section Desmotrichum, are characterized by anastomosing thickening bands. But most Dendrobiinae have water-storage cells with pleated or unpleated walls that lack these thickenings. These cells probably function to store and/or transport water and provide plants with a means of overcoming or alleviating drought stress to which some are reportedly subjected. Pleated cell walls possibly enhance flexibility and secondary thickening bands offer rigidity when the cells lose turgor during dry periods (Pridgeon, 1982). Water-storage cells have been reported in other Orchidaceae (Stern & Morris, 1992) and in some other angiosperm families, e.g. Nepenthaceae, Cyclanthaceae, and Dracaenaceae (Kny & Zimmermann, 1885; Wilder, 1985; Koller & Rost, 1988a,b; and Alfani et al., 1989). They have been referred to as internal water cells (Kr¨uger, 1883), spiral cells (Kny & Zimmermann, 1885), water-storage tracheids (Pirwitz, 1931), tracheoidal elements (Olatunji & Nengim, 1980), spirally thickened

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idioblasts (Pridgeon, 1982), parenchyma-like dead cells (Wilder, 1985), and dead parenchyma cells and water-storage tissue (Koller & Rost, 1988a,b; Alfani et al., 1989). Based on a limited sampling, Møller & Rasmussen (1984) hypothesized spherical silica bodies in all Dendrobiinae possessing stegmata. Our study supports their hypothesis and shows that in any given species, stegmata may appear in differing combinations in rhizomes, pseudobulbs, and leaves, by being present in one or more of these organs and associated with differently situated sclerenchymatous elements (Table 6). Stegmata occur in Cadetia and throughout Dendrobium (Fig. 6), except for D. rigidum and D. senile. They are absent from Pseuderia. Rhizomes in Dendrobiinae are usually distinguished from pseudobulbs because they have more and thicker-walled peripheral sclerenchyma between the groundmass region in which the vascular bundles are scattered and the epidermis, a denser arrangement of vascular bundles, fewer stegmata associated with sclerenchyma of vascular bundles, and fewer and less conspicuous (or absent) water-storage cells. Pseudobulbs in section Desmotrichum are differentiated from rhizomes in that section and from pseudobulbs in other sections by the lacunae that occur consistently at the phloem poles of many of the large internal vascular bundles (Fig. 10). Porembski & Barthlott (1988) identified 12 different velamen types in orchids. They concluded, based on their examination of species in four different sections of Dendrobium, that Dendrobiinae are characterized by what they termed a ‘Dendrobium type’ velamen, featuring cells that are typically radially elongated (i.e. anticlinal) and stabilized by helical cell wall thickenings of varying widths (Fig. 8). They did not find tilosomes, their Stabk¨orper. Our findings concur with theirs for the most part. However, the velamina of Dendrobium cunninghamii (section Macrocladium) and Pseuderia tend to comprise square to rectangular cells, rather than radially elongated cells. Additionally cells of the velamen in Pseuderia lack helical cell wall thickenings. Contrary to Porembski & Barthlott’s report we found tilosomes in D. fariniferum, D. arachnoideum, D. amplum, D. lyonii, D. cymbidioides, D. salaccense (Fig. 14), and D. malbrownii (Fig. 15), apparently a first report of these structures in Dendrobiinae (Pridgeon et al., 1983). Tilosomes, when they occur, are consistently located adjacent to passage cells of the exodermis. Possibly they function as protective plugs or barriers to transpiration and perhaps as water condensing and absorbing structures (Leitgeb, 1864; Haberlandt, 1914; Dietz, 1930; Benzing, Ott & Friedman, 1982). Velamen cell layers in Dendrobiinae range from 2 to 17 (Table 8). Only two layers occur in some species of Cadetia and Pseuderia (Fig. 18), and in Dendrobium, species in sections Diplocaulobium, Rhizobium, and Sarcopodium; there were 17 layers in Dendrobium formosum, section Formosae. In velamentous orchids, the total documented range of cell layers is 1–24 (Pridgeon, 1987). Dendrobiinae show considerable variability in numbers of velamen layers, encompassing much of the range for Orchidaceae as a whole. Stern & Morris (1992) and R¨uter & Stern (1994) outlined some reasons that might be responsible for velamen layer variability in individual species of orchids: (1) cells in velamina are not always organized in regular radial or tangential rows, making counting somewhat subjective; (2) growing roots gradually increase in diameter basipetally, and (3) velamina are frequently narrower on the side of a root attached to a substrate than on the exposed side. Numbers of velamen layers vary considerably within several sections in Dendrobiinae, even when other anatomical

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characters are consistent. Number of layers in velamina is probably not a reliable character to use in determining sectional relationships in Dendrobiinae, and Pridgeon (1982) has suggested that the number of layers of velamen is of questionable systematic value at the generic level and above. The reliability of published accounts of velamen layer number may be questionable when evidence of the methodology used to select levels for counting along the length of the root is lacking (R¨uter & Stern, 1994). Conspicuous secondary cell wall thickenings are confined to the proximal portions of the anticlinal walls and inner tangential walls of the innermost layer of velamen cells in some taxa (Table 8). Because of the overall shape of the thickened regions, we have designated these as V-thickenings (Fig. 12), and they may be reported here for the first time. Although they do not define these thickenings specifically, Solereder & Meyer (1930) note that the innermost layer of the velamen may show a characteristic wall structure at its tangential boundary adjacent to the exodermis. Velamen cells in which the walls are V-thickened are present in species of sections Rhizobium, Sarcopodium, Dendrocoryne, and Latouria, and in Dendrobium aphyllum in section Dendrobium, D. lamellatum in section Platycaulon, D. secundum in section Pedilonum, and D. malbrownii in section Monanthos. In the thin longitudinal walls of dead (long) exodermal cells, Stern et al. (1993) described tenuous scalariform thickenings, apparently for the first time, in all taxa of tribe Cranichideae (Spiranthoideae). They considered these cell wall modifications to function as supporting and rigidifying structures that prevent deformation of the thin-walled exodermal cells characteristic of Cranichideae. It was not known then whether these structures were confined to Cranichideae, and our observations here indicate they are not. Numerous scalariform bars are characteristic of the longitudinal walls of dead thick-walled exodermal cells in all taxa of Dendrobiinae except Pseuderia. Because these scalariform thickenings also occur in the thick-walled exodermal cells of Dendrobiinae, one wonders, then, if their function is really related to support as suggested by Stern et al. (1993), and indeed, what the function of these structures is.

CLADISTICS

A cladistic analysis of 69 taxa in Dendrobiinae was conducted using the mhennig* (retaining equally parsimonious trees) and bb* (extended branch-swapping) options of Hennig86, version 1.5 (Farris, 1988). Operational taxonomic units (OTUs) represent all genera and sections in Dendrobiinae available in this study. Sections for which there are presumed synapomorphies, i.e. Desmotrichum, Sarcopodium, Phalaenanthe, Spatulata, and Rhopalanthe based on a survey of the literature, especially Schlechter and Seidenfaden (1980, 1985), as well as Cadetia and Pseuderia, were represented by a single OTU. Sections comprising dubiously monophyletic groups were represented by all available taxa; D. capillipes, D. falconeri, and D. palpebrae were not included because of large numbers of missing data. Seventeen anatomical characters derived from this investigation were employed (Tables 9, 10) and were polarized using outgroup analysis (Stevens, 1980; Maddison, Donoghue & Maddison, 1984; Wiley et al., 1991). Section Grastidium was used as the functional outgroup, because it is hypothesized to be paraphyletic relative to the remaining taxa

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TABLE 6. Stegmata. Leaf Vascular bundles Genus Section Cadetia Pterocadetia Cadetia Dendrobium Desmotrichum Goniobulbon Diplocaulobium Bolbidium Rhizobium Sarcopodium Dendrocoryne Latouria Inobulbon Callista Dendrobium Platycaulon Pedilonum Brachyanthe

Stem Fibre bundles Adaxial

+ + + + +, except D. rigidum + + + + + +, except D. senile + + +

Abaxial absa abs

+, C. taylori only + –

+, C. taylori only + +

abs – +

Vascular bundles

+ abs abs abs abs abs abs abs abs abs abs abs

–

+ + + + +, only D. lichenastrum + + + + + +, except D. senile + + +

in Dendrobiinae (Yukawa et al., 1992) and because it exhibits a relatively simple vegetative anatomical structure presumed to be plesiomorphic. Choice of the appropriate outgroup from outside the Dendrobiinae is highly controversial (Robert L. Dressler, pers. comm.) and beyond the scope of this work, for the alternatives, Eria, Bulbophyllum, or the Malaxis group, are also species-rich with at least several hundred taxa each. These three groups, like Dendrobiinae, contain wide morphological, and quite possibly anatomical, diversity; the phylogenetic relationships within each are very poorly understood. Thus, the polarization of characters by using any one or all of these three groups as the outgroup would be exceedingly problematic. All characters were readily divisible into discrete states, thus avoiding arbitrary decisions relating to state delimitation (Stevens, 1991). Anatomical features that had to be excluded from the cladistic analysis because discrete states could not easily be delimited include: foliar and cauline cuticle thickness and surface texture, stomatal configuration, guard cell dimensions, foliar and cauline epidermal cell wall thickness, foliar chlorenchyma seriation, numbers of cell layers in velamen and cortex, and numbers of protoxylem arms. Character codings are presented in Table 9. The preliminary phylogenetic analysis, resulted in the discovery of 1379 + equally parsimonious trees of 83-steps, consistency index (CI) of 0.30, and retention index (RI) of 0.75. The strict consensus tree is presented in Figure 19. Much variability was observed in the topology of the generated cladograms, especially in the lower nodes, and this resulted in the very large polytomy at the base of the strict consensus tree. This variability is indicative of the high level of homoplasy evident in many anatomical characters in Dendrobiinae. Topological variability may also be due to intrataxon heterogeneity and missing data for a number of included taxa. All generated cladograms indicate that Dendrobium is paraphyletic if the other genera ascribed to subtribe Dendrobiinae sensu Dressler are recognized. Cadetia and Pseuderia are embedded in Dendrobium in all 1379 generated cladograms. Pseuderia is nested within Dendrobium in the lower unresolved portion of the strict consensus tree,

ANATOMY AND SYSTEMATICS OF DENDROBIINAE (ORCHIDACEAE)

TABLE 10. Character matrix for taxa used in cladistic analysis. Species arranged according to Schlechter. V=variable character state; ?=unknown character state. Taxon (Section)

12345

67890

12345

67

Dendrobium salaccense (Grastidium) Cadetia taylori Dendrobium macraei (Desmotrichum) D. chrysotropis (Goniobulbon) D. arachnoideum (Diplocaulobium) D. fariniferum (Diplocaulobium) D. guttulatum (Diplocaulobium) D. pachyphyllum (Bolbidium) D. teretifolium (Rhizobium) D. lichenastrum (Rhizobium) D. cymbidioides (Sarcopodium) D. jonesii (Dendrocoryne) D. kingianum (Dendrocoryne) D. macropus (Dendrocoryne) D. speciosum (Dendrocoryne) D. tetragonum (Dendrocoryne) D. johnsoniae (Latouria) D. macrophyllum (Latouria) D. munificum (Inobulbon) D. amethystoglossum (Callista) D. chrysotoxum (Callista) D. densiflorum (Callista) D. griffithianum (Callista) D. lindleyi (Callista) D. thyrsiflorum (Callista) D. albosanguineum (Dendrobium) D. aphyllum (Dendrobium) D. chrysanthum (Dendrobium) D. dixanthum (Dendrobium) D. fimbriatum (Dendrobium) D. findlayanum (Dendrobium) D. loddigesii (Dendrobium) D. moschatum (Dendrobium) D. nobile (Dendrobium) D. parishii (Dendrobium) D. pendulum (Dendrobium) D. primulinum (Dendrobium) D. pulchellum (Dendrobium) D. senile (Dendrobium) D. signatum (Dendrobium) D. tortile (Dendrobium) D. lamellatum (Platycaulon) D. platygastrum (Platycaulon) D. bracteosum (Pedilonum) D. bullenianum (Pedilonum) D. secundum (Pedilonum) D. smillieae (Pedilonum) D. alterum (Brachyanthe) D. hercoglossum (Brachyanthe) D. compactum (Stachyobium) D. delacourii (Stachyobium) D. williamsianum (Phalaenanthe) D. canaliculatum (Spatulata) D. fellowsii (Eleutheroglossum) D. antennatum (Spatulata) D. cruentum (Formosae) D. dearei (Formosae) D. formosum (Formosae)

00000 00111 00100 00111 00101 ????? 00101 00110 10110 10110 01V01 00001 00000 00000 00111 00001 00100 00000 00101 00000 00111 00110 00111 00111 00110 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00000 00110 00000 00000 00000 00000 00000 00110 00000 00VVV 02000 02000 02000

00000 100VV V0100 00011 01100 ????? 01100 20010 2002? 2002V 0V000 00010 0000? 00011 0000? 00010 00000 0000V 10010 0001? 00010 0001? 00000 00000 0001? 0001? 0001? 0000? 00010 0000? 0001? 20000 0001? 0000? 0001? 0000? 0001? 0001? 0002? 00000 00010 00000 00001 00000 00010 00011 00000 00000 00000 00000 00000 00000 00000 0000? 000V0 0001? 00010 00000

00000 0010V 10100 00100 00000 00000 00000 00101 V1112 V1112 1021V 0011V 0011V 00100 0010V 00110 00112 00110 00??? 00100 00100 00100 00100 00100 00100 00101 00110 00100 0010V 00100 00100 00100 00100 00100 00100 00100 00100 00100 0010V 00100 00??? 00110 00100 00100 00100 0011V 00100 00100 0010V 0010V 00101 00101 00100 00100 00100 0010V 00100 00100

00 01 0V 21 01 01 01 11 00 VV 00 10 00 20 00 10 00 01 ?? 10 00 10 11 11 01 01 00 01 21 20 00 21 20 10 00 01 00 20 00 00 ?? 01 10 V0 01 01 10 01 11 21 21 V? 00 01 V0 01 01 20

137

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M. W. MORRIS ET AL.

TABLE 10. (continued) Taxon (Section)

12345

67890

12345

67

D. sanderae (Formosae) D. schuetzei (Formosae) D. virgineum (Formosae) D. crumenatum (Rhopalanthe) D. acerosum (Aporum) D. acinaciforme (Aporum) D. anceps (Aporum) D. leonis (Aporum) D. cunninghamii (Macrocladium) D. malbrownii (Monanthos) Pseuderia smithiana

02000 02000 02000 00VV0 20010 20010 20010 20010 00000 00000 00000

0001? 0000? 0001? 00100 201?0 20120 20100 2012? 00022 01112 00002

00100 00100 0010V 00100 01100 01100 01100 01100 00?00 00212 00100

11 11 00 0V 01 V1 01 01 00 00 1V

while Cadetia is placed consistently with certain specialized species (Fig. 19). All analyzed taxa possibly form a monophyletic group based on the synapomorphy of tilosomes absent in roots. Tilosomes reappear in only three taxa in the analysis: two species of section Diplocaulobium, three species of section Sarcopodium (an autapomorphy for this section that corresponds to the genus Epigeneium recognized by Dressler and others), and one species of section Monanthos (an autapomorphy). The genus Epigeneium (as section Sarcopodium) also is nested consistently within Dendrobium (Fig. 19). Finally the genera Flickingeria (as section Desmotrichum) and Diplocaulobium (only section Diplocaulobium) form a clade with Dendrobium section Rhopalanthe in all

Figure 19. Strict consensus of 1379 + trees. Sectional names are enclosed in parentheses.

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discovered cladograms; all three groups possess the synapomorphies of an adaxial hypodermis and abaxial fibre bundles. Two of the three Diplocaulobium species (Dendrobium fariniferum and D. arachnoideum) are diagnosed by the reversal to tilosomes in roots. Dendrobium arachnoideum and D. guttulatum are characterized by heterogeneous mesophyll and adaxial fibre bundles. Only roots were available for study in D. fariniferum. Section Goniobulbon, species of which have been placed in Diplocaulobium when this genus is recognized, is placed consistently in a specialized clade that also contains members of sections Dendrocoryne, Callista, Inobulbon, Eleutheroglossum, Pedilonum, Rhizobium, and Aporum (Fig. 19) and, therefore, may not be closely related to section Diplocaulobium. Section Goniobulbon (represented by D. chrysotropis) lacks the derived features of abaxial fiber bundles in leaves, as well as tilosomes in roots. A clade supported in all discovered cladograms includes the single taxon, D. pachyphyllum, representing section Bolbidium, the four available species of section Aporum, and the two included species of section Rhizobium (Fig. 19). This clade is supported by the following synapomorphies: (1) an abaxial hypodermis, (2) waterstorage cells with pleated walls in mesophyll, and (3) anticlinal endodermal cells. The four species of section Aporum and the two included species of section Rhizobium share the synapomorphy where mostly only the abaxial epidermis is exposed. In the species of section Aporum, a mesophyll lacuna is lacking and abaxial fibre bundles are present in the leaf. Dendrobium acinaciforme and D. leonis share the derived character where foliar midvein stegmata are lacking. Synapomorphies for section Rhizobium include: (1) only or largely abaxial epidermis exposed and presence of a mesophyll lacuna or incipient lacuna, (2) abaxial hypodermis, (3) pseudobulbs absent, and (4) waterstorage cells with pleated walls (Stern et al., 1994). Another clade, comprising D. griffithianum, D. lindleyi, and D. chrysotoxum of section Callista, is supported by heterogeneous foliar chlorenchyma. A clade comprising D. macrophyllum (section Latouria) and D. lamellatum (section Platycaulon) is weakly supported by innermost velamen cells V-thickened. The linking of D. malbrownii with D. secundum is also only weakly supported. A small clade seen in the strict consensus tree comprises Dendrobium senile (section Dendrobium) and D. cunninghamii (section Macrocladium); the monophyly of this group is supported by the absence of foliar midvein stegmata. A group comprising Dendrobium delacourii (section Stachyobium) and D. williamsianum (section Phalaenanthe) is supported by the shared derived characters of exodermal cell walls <-thickened and endodermal cells periclinal. A noteworthy clade evident in all the cladograms discovered in this analysis includes five species of section Callista (D. griffithianum, D. lindleyi, D. chrysotoxum, D. densiflorum, and D. thyrsiflorum), the genus Cadetia, D. canaliculatum (section Spatulata), D. speciosum (section Dendrocoryne), D. smillieae (section Pedilonum), D. chrysotropis (section Goniobulbon), D. munificum (section Inobulbon), and the included species of sections Rhizobium and Aporum. The group is diagnosed by an abaxial hypodermis. Dendrobium densiflorum and D. smillieae may form a clade based on their anticlinal endodermal cells, which may have evolved independently in the clade containing Dendrobium griffithianum and D. lindleyi. The monophyly of section Formosae is strongly supported in most but not all cladograms. This clade is diagnosed by the following synapomorphies: (1) leaf hairs frequently paired and with long glandular extensions and (2) pith sclerenchymatous. The second character reverses to parenchymatous pith in D. formosum and D. virgineum. Dendrobium sanderae, D. cruentum, D. dearei, and D. virgineum share the derived

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character of foliar midvein stegmata at both xylem and phloem poles. The latter three species also exhibit a reversal to isodiametric endodermal cells.

CONCLUSIONS

Both Cadetia and Pseuderia are apparently nested within the cladistic structure of Dendrobium if section Grastidium is used as the functional outgroup. Cadetia and Pseuderia share the derived character of absence of tilosomes in roots with most other members of Dendrobiinae, despite reversals in sections Diplocaulobium, Sarcopodium, and Monanthos. It is uncertain which of Schlechter’s sections of Dendrobium are most closely related to Cadetia and Pseuderia, because the placement of these taxa varies in the discovered trees. Likewise, most of the sectional relationships remain unresolved (Fig. 19). If Flickingeria and Diplocaulobium are recognized as separate genera, then Dendrobium becomes even more paraphyletic. Flickingeria (section Desmotrichum) and Diplocaulobium (only section Diplocaulobium) are hypothesized to be closely related because each possesses (1) an adaxial hypodermis and (2) abaxial fibre bundles. This evidence supports Schlechter’s idea of relationships for these groups. His sections Desmotrichum and Diplocaulobium are also considered to be monophyletic based on anatomical data. Section Rhopalanthe may also be a part of the Desmotrichum-Diplocaulobium clade, but this placement may, in part, result from the several character states of this taxon that were coded as variable (Table 10). In contrast, macro- and micromorphological data support a relationship between section Rhopalanthe and section Aporum (Schlechter, 1912; Yukawa et al., 1990, 1992) and possibly even section Bolbidium (Yukawa et al., 1990, 1992). Members of both sections Aporum and Bolbidium have an abaxial hypodermis, and species of section Aporum also have abaxial fibre bundles (Tables 4, 5). If Epigeneium (Schlechter’s section Sarcopodium) is recognized as a genus, Dendrobium, again, becomes non-monophyletic. Our evidence supports the view that section Sarcopodium is a monophyletic group, thus corroborating Schlechter’s opinion. The relationship between sections Rhizobium and Aporum is noteworthy, because among all the taxa studied only in the leaves of species in these groups is the exposed epidermis predominantly or exclusively abaxial. There is at least a degree of artificiality in Schlechter’s subgeneric classification. In the strict consensus tree, the clade comprising section Bolbidium (placed in subgenus Athecebium) and the four available species in section Aporum (placed in subgenus Xerobium) illustrates the presumably non-monophyletic circumscription of his subgenera (Fig. 19). These sections form a monophyletic group based on the synapomorphies of an abaxial hypodermis, water-storage cells with pleated walls in mesophyll, and anticlinal endodermal cells (Tables 4, 6, 9). If section Rhopalanthe (subgenus Rhopalobium) is also related to this group as indicated by Yukawa et al. (1990, 1992), then the circumscription of his subgenera may be even more artificial than it already appears. Sections Stachyobium and Phalaenanthe may be closely related, because they form a small clade diagnosed by the common possession of <-thickened exodermal cells and periclinal endodermal cells (Table 8). Schlechter placed these sections fairly close to

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each other (along with section Fytchianthe, not represented in our investigation), and anatomical data tend to support his hypothesized relationships. The anatomy of subtribe Dendrobiinae reflects the high degree of morphological diversity. However, many of these anatomical characters are homoplasous. When these anatomical data are interpreted with a view toward understanding the systematic relationships among the various genera that have been recognized and proposed by Dressler and Schlechter, they indicate that Dendrobium, as currently circumscribed, is non-monophyletic (Fig. 19). It is difficult to determine the phylogenetic relationships of many of Schlechter’s sections, first because several are probably non-monophyletic, and are therefore quite indeterminate, and second because there appears to be a high level of homoplasy. Micromorphological and preliminary molecular work by other investigators (Yukawa et al., 1990, 1992) also point to this conclusion. The lack of resolution seen in the strict consensus tree illustrates this difficulty (Fig. 19). Until the relationships among taxa in Dendrobiinae are more fully resolved, we suggest that the species included in this analysis be considered as members of a single large genus, Dendrobium, without the recognition of segregate genera. Schlechter’s sectional classification, with some modification, may be retained for the present, if only for convenience. We suggest that a more detailed understanding of the phylogeny of Dendrobiinae will require cladistical analyses employing characters from morphology, micromorphology, anatomy, and DNA. ACKNOWLEDGEMENTS

We appreciate the constructive criticisms and careful reading of an early draft by Terry W. Lucansky, Norris H. Williams, Thomas J. Sheehan, and Francis W. Zettler, faculty in plant sciences at the University of Florida. Robert L. Dressler, Florida Museum of National History, Gainesville, and Phillip J. Cribb, Royal Botanic Gardens, Kew, kept us posted on recent developments in the classification of Dendrobiinae. At the Royal Botanic Gardens, Kew, Alec M. Pridgeon provided overlooked references and reviewed a draft of this paper, Mary Gregory assembled pertinent literature and gave us copies of papers not readily available, and Joyce Stewart and Sandra Bell were helpful in supplying research materials from Kew’s living collections. John Atwood and other staff of the Marie Selby Botanical Gardens donated specimens from their collections, and Marilyn Le Doux, Missouri Botanical Garden, helped with material from Garden greenhouses. We obtained fluidpreserved plants of Dendrobium cunninghamii from New Zealand through the courtesy of Alan Mark and Lyn Forster, University of Otago. Saula Vodonaivalu, University of the South Pacific, collected fresh material of the elusive Pseuderia, and we appreciate this special effort. Suzette Morris prepared all leaf surfaces for study, and Sherry Morris typed the original draft. Many of our specimens of Dendrobium from the collection of WLS were originally provided as living plants by the late Fred Fuchs, Jr. of Naranja, Florida. The National Science Foundation of the United States funded a portion of this research under grant DEB-9006474 to WLS. American Orchid Society/11th World Orchid Conference Fellowships were awarded to MWM during 1989 and 1990. We thank David A. Jones, Chairman, Department of Botany, University of Florida, for providing a partial stipend for Suzette Morris and for making department facilities available to us.

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