A revision of the genus Elodea (Hydrocharitaceae)

Aquatic Botany, 21 (1985) 111--156 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

111

A REVISION OF THE GENUS E L O D E A (HYDROCHARITACEAE)

CHRISTOPHER

D.K. C O O K

and K A T H A R I N A

URMI-KONIG

Institut ffir Systematische Botanik der Universit~it Zr~rich, Zollikerstrasse 107, 8008 Z~rich (Switzerland)

(Accepted for publication 12 October 1984)

ABSTRACT

Cook, C.D.K. and Urmi-KSnig, K., 1985. A revision of the genus Elodea (Hydrocharitaceae). Aquat. Bot., 21: 111--156. A taxonomic revision of the genus Elodea (Hydrocharitaceae) is presented with full descriptions of each species with diagnoses, synonyms with typifications, distribution maps and illustrations also containing information on ecology, floral biology, anatomy, morphology, chromosomes, genetics, physiology and applied aspects, with an extensive bibliography. Five species of Elodea are recognised and one (E. granatens~s Humboldt and Bonpland) is replaced in the genus Apalanthe. All species are from the N e w World, but some have become widely naturalized in the Old World. N e w morphological, ecological, distributional, genetic and cytological information is incorporated.

INTRODUCTION In a series of papers St. J o h n (1920, 1962, 1963, 1964, 1965) published a world-wide account of the genus Elodea. He recognised 17 species, 9 of which he described as new. We have f o u n d these papers to be unsatisfactory. The delimitation of species is a personal m a t t e r which is more or less sacrosanct and hardly open to scientific testing. However, St. J o h n ' s publications contain numerous errors particularly in the citation o f herbarium specimens (often the location of the herbarium sheet is incorrectly cited).We have found numerous cases of the specimen being determined by St. J o h n under one name and t h e n cited under another. The published illustrations are very diagrammatic and are often inaccurate. Some of the 'leads' in the keys are absurd, e.g. "dioecious species of which only one sex is k n o w n " followed by "pistillate flowers u n k n o w n " . A more serious objection is t h a t frequently the measurements printed in the descriptions do n o t fit the specimens St. J o h n examined, and in some cases even exclude the h o l o t y p e , also some t y p e specimens are, a n y w a y , incorrectly chosen. These mistakes contribute to a general mistrust of St. J o h n ' s t a x o n o m i c judgements. We have reduced the 17 species recognised by St. J o h n to 5 species of E l o d e a and one (E. granatensis H u m b o l d t and Bonpland) is replaced 0304-3770/85/$03.30

© 1985 Elsevier Science PublishersB.V.

112

in the genus Apalanthe. However, we realise that our revision is somewhat equivocal and that for a definitive account considerable field work, particularly in North America, is necessary. We have made every effort to reveal rather than conceal our taxonomic doubts. M ATER I ALS AND METHODS

The following species have been maintained in cultivation in the University of Ziirich botanic gardens: Elodea canadensis Michaux (9) from Europe and N. America (Alabama and Minnesota); E. nuttallii (Planchon) St. John (~ and q) from Europe and N. America (Indiana); E. potamogeton (Bertero) Espinosa (d and Q) from Bolivia. We have studied herbarium specimens from the following herbaria: Unidad Bot~inica Agricola del I.N.T.A., Buenos Aires (BAB); Museo de Botanica y Farmacologfa "Juan A. Dominguez" Buenos Aires (BAF); British Museum of Natural History, L o n d o n (BM); UeberseeMuseum, Bremen (BREM); National Herbarium of Canada, Ottawa (CAN); Museo Bot~nico, Facultad de Ciencias E.F., Cordoba (CORD); the Deaver Herbarium, Flagstaff, Arizona (DHA); Royal Botanic Garden, Edinburgh (E); Conservatoire et Jardin botanique, Gen~ve (G); Gray Herbarium of Harvard University, Cambridge (GH); Royal Botanic Gardens, Kew (K); Missouri Botanical Gardens, Saint Louis (MO); New York Botanical Garden, Bronx (NY); Naturhistoriskariksmuseet, Stockholm (S); Istituto de Bot£nica Darwinion, San Isidro (SI); Herbarium of the University of California, Berkeley (UC); Smithsonian Institution, Washington (US); Peter Wolff, (private herbarium) Dudwefler, W. Germany (WOLFF); Washington State University Herbarium, Pullman (WS); Universit~it, Ziirich (Z); EidgenSssische Technische Hochschule, Ziirich (ZT). The majority of the plants preserved in herbaria are without flowers which makes certain identification difficult or, in many cases, impossible. The information presented in our descriptions and the origins of the "dots" presented on the distribution maps are based only on specimens of certain identity. These specimens bear"!" on our identification labels; the rest of the herbarium material we examined has only an opinion on the identity labels. This material is n o t incorporated into this account. TAXONOMY

ELODEA A. Michaux, F1. Bor.--Amer., 1: 20. 19 March 1803. Type: E. canadensis A. Michaux; holotype: Canada "Elodea oblongifolia, Environs de Montreal", Michaux (P). = Anacharis L.C.M. Richard, M~m. Classe Sci. Math. Phys. Inst. Imp. France, 1811(2): 7, 61. dated 1812 published 1814. Type: A. callitrichoides: Uruguay "hab. circa Montevideo", Commerson (P~IU n.v.). = Diplandra Bertero, Mercurio Chileno, 13: 612. 15 April 1829. Type: D. potamogeton; Chile, "en las aguas claras de las acequias de la Quinta, Corcolen y Taguatagua", Bertero (lectotype: TO n.y.).

113

--Philotria Rafinesque, Amer. Monthly Mag. Crit. Rev., 2: 175. Jan. 1818; nom. illeg., based on Elodea A. Michaux 1803. --Udora Nuttall, Gen., 2: 242. May--June 1818; nom. illeg., based on Elodea A. Michaux 1803. We do not consider the families Vallisneriaceae Dumortier and Elodeaceae Dumortier worthy of recognition. We assign Elodea to the family Hydrocharitaceae, subfamily Vallisnerioideae, tribe Hydrillaeae (= Anachariteae). Dioecious or rarely monoecious, submerged, fresh-water, perennials. Roots: simple, adventitious, developing only at nodes bearing lateral branches. Stems: either creeping and somewhat rhizomatous or erect, slender, terete, up to ca. 4 m or longer, often freely branched near the base, sparingly branched above until near the water surface, where often many branches develop; branches resemble the main stem, arising from internodes of normal appearance (unlike double internodes in Egeria); somewhat bud-like turions develop in E. canadensis and E. potamogeton. Prophylls (see p. 116) paired, lateral or slightly oblique, deltate to ovate or narrowly ovate, acute to apiculate, transparent or pale green. Foliage leaves cauline, usually paired below, in whorls of 3 (rarely up to 6), successive internodes rotated through 60 ° (thus, leaves appearing as if arranged in 6 rows), ovate to linear or narrowly oblong, spreading or recurved, with scattered dark cells often arranged in longitudinal lines, marginal bands of fibres present (visible under polarized light); midrib usually distinct; margin serrulate to denticulate; teeth rarely visible to the naked eye; apex obtuse to acute, usually shortly acuminate, and usually bearing more than one terminal spine cell. Squamulae intravaginales 2 to each leaf, ovate to transversely elliptic, translucent, 0.15-0.44 mm long, 0.1--0.28 mm wide. Spathes consisting of 2 lateral and conduo plicate, united bracts each acute to mucronate at the apex; sessile, subglobose or obovoid to cylindrical with expanded distal portions containing 1 or very rarely 2 flowers, born solitary at nodes and never at consecutive nodes. Male flowers sessile to long-pedicellate, remaining attached or becoming freefloating, usually opening on the surface of the water. Male sepals 3, free, suborbicular to narrowly oblong or narrowly elliptic, green with lilac to purple stripes or patches or purple, usually reflexed, at anthesis with distinct midrib and hyaline margins. Male petals 3, free, rudimentary or usually somewhat longer and distinctly narrower than the sepals, very thin and flimsy, deliquescent, whitish-translucent sometimes with a purple vein or tip. Stamens mostly 9 (or in bisexual flowers usually 3), in alternating whorls of 3; filaments very short, the inner at least usually united at base forming a column; anthers basifixed, with 2 microsporangia, opening adaxially (after anthesis petal-like); endothecium without thickenings; tapetum periplasmodial; pollen single or in tetrads, elongate-globose, 3-ceUed, inaperturate, the surface irregularly reticulate with small spines on the junctions {Fig. 1). Nectaries absent. Pistillodia usually absent, occasionally rudimentary. Female sepals and petals like those of the male, but usually somewhat smaller (petals

114

a

~

.......'

b

'

d

I

z

e

,

g

'

"

h

,

"

c

,

,

'"'

f

i

,,

,

,

'

Fig. 1. Elodea: (a)E. callitrichoides, pollen grain (scale bar: 40 tam); (b)E. callitriehoides, surface of pollen grain (scale bar: 2 pm); (c)E. callitrichoides, edge of pollen grain (scale bar: 2 tam); (d) E. nuttallii, pollen tetrad (scale bar: 40 pro); (e) E. nuttallii, surface of pollen grain (scale bar: 2 tam); (f) E. potamogeton, surface and edge of pollen grain (scale bar: 4 tam); (g) E. bifoliata, surface of pollen grain (scale bar: 4 ~m); (h) E. canadensis, surface of pollen grain (scale bar: 2 #m); (i) E. canadensis stomata on surface of sepal of female flower (scale bar: 40 pro). Origin of material: (a--c) Argentina, Buenos Aires, Burkart 15592 (ZT); (cl,e,i) Botanic Garden Z~rich; (f) Bolivia, Khota Khota, Beck cult. Z~irich; (g) New Mexico, Rio Arriba Co., Standley 8274 (U.S.); (h) Oregon, Klarnath Co., Abrams 9719 (MO).

115

are usually wider, but often hidden from view under the curved styles). Staminodia 3, free, antesepalous, filiform, rarely exceeding 2 m m long, greenish- white below, papillose and lilac above, persisting after the styles have withered. Ovary inferior, cylindric and attenuated above into an elongate hypanthium, of 3 united carpels, 1-1ocular with 3, parietal, papillose, septal ridges; styles 3, antepetalous, conduplicate, recurred, entire or 2lobed, somewhat flattened, laterally papiUose, white with white to purple papillae; ovules up to 10, but usually less, orthotropous, erect with short funiculus mostly inserted at base of placenta, but some parietal;embryo sac polygonum-type; embryo macropodous and straight. Fruit ellipsoidal to ovoidal, thin-walled (seeds showing through) with apical beak, irregularly dehiscent. Seeds fusiform with micropylar beak; testa smooth or with short basal hairs or with long hairs up to 1 m m long with spirally thickened walls or glabrous; the base of the beak smooth or with wart-like cells. DIAGNOSTIC FEATURES (with regard to other genera of the Hydrocharitaceae)

d K3 C3 A3+3+3 NO GO; ~ K3 C3 A3s NO G(3). Leaves cauline in whorls (mostly of 3), with large dark~oloured cells; prophylls lateral; squamulae intravaginales ovoid to depressed orbicular, entire; petals flimsy, narrower, but sometimes longer than sepals; staminodia of female flowers, simple, white to pale violet; styles entire or bifid, recurred; seeds mostly basal, erect with beak-like micropyle; testa with long spirally thickened hairs or glabrous. DISTRIBUTION The native range is temperate North America and temperate to subtropical South America. Elodea is absent from Central and tropical America where it is "replaced" by the genus Apalanthe. It is widely introduced and has be~ come naturalized in Eurasia and Australasia. ANATOMY AND MORPHOLOGY The publication of Caspary (1858a) remains the most detailed account of the anatomy and morphology of Elodea. The summary of Tomlinson (1982) reviews the anatomy of the whole Anachariteae without always making clear distinctions between the genera. Root: Van Tieghem (1870--1871) and Van Tieghem and Douliot (1888) confirm Caspary's observation that the cell-wall thickenings of the central protoxylem are absorbed very early in development leaving a central liquidfilled lacuna. The metaxylem has tracheary elements only; therefore, the mature root has no vessels (Cheadle, 1942; Ancibor, 1979). The protomeristem of the root apex (Kadej, 1966) and the development of the root hairs (Leavitt, 1904; Dale, 1951) are like those of Egeria densa Planchon described by Cook and Urmi-KSnig (1984).

116 Stem: The anatomical term "Casparian strips or bands" for endodermal thickenings goes back to the work of Caspary (1858a) on E. canadensis. His observation that the wall thickenings of the protoxylem elements are absorbed early in development has been confirmed by Schenck (1886) and Dale (1957), and the remark o f Cheadle (1942) that there are "no vessels in the stem" is correct only for mature stems. Caspary (1858a) gave the first topographical description of the branching system describing the lateral and subopposite prophylls of axillary shoots and noted that the "upper" or earlier prophyll bears a bud, b u t unlike Egeria double nodes do not develop; Rftter (1918) confirmed Caspary's observations. According to Brunaud (1976, 1977) the initiation of the lateral shoots and inflorescences occurs in the 6th--12th leaf from the shoot apex. The lateral shoot appears in the axil of a leaf-primordium and, at first, develops slowly in contrast to the inflorescence which develops quickly and soon extends beyond the apex of its mother axis. Wilder (1975) suggested that the sterile shoots o f E. canadensis are homologous to the stolons of Vallisneria and Limnobium (Cook and Urmi-K~nig, 1983); this theory needs further study. Turions are found in E. canadensis and E. potamogeton, but they are rather primitive in form, compared to those of Hydrilla or Hydrocharis, and possess no distinct abscission layer, no dormancy and occasionally they restart growth while still attached to the mother plant. Leaf: The anatomy has been adequately described by Caspary (1858a), Schenck (1886), Solereder (1913), Pfeiffer (1919) and Ancibor (1979). In contrast to Egeria the leaves of Elodea have submarginal fibres and the idioblasts are brown. Vessels are found only in the early stages of leaf development and then they are confined to the base of the bundles. Each leaf receives 2 bundles which unite to form a single trace without any leaf gaps in the stele. Lance-Nougar~de and Loiseau (1960) remark on the similarity in the development of Elodea leaves and the microphylls of the Psilophytales: the procambial traces in both groups have no connection to the initial ring. The first leaves (prophylls) on each axis are subopposite, scale-like and lie in a lateral or sublateral position. After the prophylls there are usually some internodes with paired short leaves before the normal foliage leaves develop (Fig. 7b). Lyr and Streitberg (1955) did not find any discrete hydropoten. Squamulae intravaginales: the squamulae are 2 cell-layers thick and paired in leaf axils. The cells of the squamulae secrete a mucilage which according to Schilling (1894), at first, collects under the cuticle; at this stage they are almost spherical. Before the leaf is fully developed the cuticle bursts liberating a slimy mucus. Inflorescence: Caspary (1858a) noted that spathe consists of 2 united, lateral bracts with free apices which Brunaud (1977) considered to be homologous to the prophylls of lateral shoots. We have found no evidence that the inflorescence and its subtending leaf belong to the next upper node and we have not regularly found 2-leaved whorls distal to 4-leaved fertile whorls. Wylie (1904) described the inflorescence as loose and indeterminate

117 with the single-flowered units representing partial inflorescences. Kaul (1970) considered single-flowered inflorescences to represent the ultimate reduction in the Hydrocharitaceae. Flower: All floral parts are arranged in alternating whorls of 3, which is reflected by the vascularization of the flower (Kaul, 1968). The sepals bear stomata (Fig. li); they are not found on any other part of the plant. The stomata are without neighbouring cells at their tips. The staminodia are almost certainly of staminal origin as they occasionally bear imperfect anthers. Bisexual flowers, when they occur, are clearly female with fertile staminodes; however, style or stigma-like structures are sometimes seen in male flowers (illustrated by Douglas, 1880). Wylie (1904) found that these stigma-like structures contained pollen-tubes. Jitariu (1952) described the gynoecium as paracarpous; the morphology and anatomy of fruit and seeds have never been described in detail. In E. nuttallii the male flower buds are subsessile and absciss in the bud stage. Elodea canadensis has stalked male flowers that absclss shortly before or during anthesis, the other species have male flowers that remain attached to the mother plant during anthesis. FLORAL BIOLOGY The pollination mechanisms are reasonably well documented (E. callitrichoides: Hauman-Merck (1909,1913), Ernst-Schwarzenbach (1934, brief note, 1945a); E. nuttallii: Wylie (1904), Strasburger (1910), Woodward (1919), Ernst-Schwarzenbach (1934, brief note, 1945a); E. potamogeton: Espinosa Bustos (1927)). We have examined E. canadensis 9, E. nuttallii d and vt, and E. potamogeton d and ~ in cultivation in ZRrich. The flowers of both genders are borne singly in spathes. The female flower breaks through the apex of the spathe and is carried to the surface of the water on an elongate hypanthium. At anthesis the sepals spread and, as they are unwettable, float on the surface of the water; the petals are very flimsy and are often forced under water below the recurred styles. The styles spread between the sepals and then recurve distally with the tips usually becoming submerged. In all species, except E. nuttallii and some of its hybrids, the male flowers are borne on long pedicels. The flower buds emerge through the distal parts of the spathes and the pedicels, unlike the hypanthia of the females, often continue to elongate long after the flowers have reached the surface of the water. In E. nuttallii the pedicel abscisses, while still within the spathe, and the bud is brought to the surface with a gas bubble like Hydrilla (Cook and Li~Bnd, 1982). However, unlike Hydrilla the flower opens gradually and some anthers dehisce while still in the gas bubble under water. The male flowers open in daylight on the surface of the water. In E. nuttallii the sepals and petals reflex and the flowers float on the recurved tips of the sepals, the petals are very flimsy and reduced and play no active role in pollination. The stamens are erect before dehiscence, they then

118

dehisce in a more or less horizontal position and after the pollen has been shed they lie appressed to the reflexed perianth; the pollen grains which are shed in relatively massive tetrads are unwettable and reach the stigmas by travelling over the water surface, the way to the stigmas is helped by local changes in surface tension between the spreading and unwettable sepal segments. Ernst-Schwarzenbach (1945a) reported that the stamens are originally extrorse and through a 180 ° torsion they become introrse; we have failed to see this torsion. The male flowers of E. canadensis usually become detached from the mother plant, the pedicel is fragile and breaks during or shortly after anthesis, the male flowers of the other species of Elodea remain attached to the mother plant throughout anthes/s. In contrast to E. nuttaUii, the sepals and petals first spread on the water surface and later become reflexed. The anthers dehisce in a more upright position and the inner anthers usually remain erect after dehiscence and superficially resemble petals. Some pollen remains on the spreading perianth segments and between the stamens, but our observations lead us to believe that the effective pollen transfer is on the surface of the water like in E. nuttalliiand not by transfer of complete male flowers as Ernst-Schwarzenbach (1945a) reports. W e have also failed to see the 180 ° torsion of the stamens in this group of species as reported by Ernst~Schwarzenbach (1945a), we also disagree that the flowers open suddenly, anthesis is a gradual process. In E. potamogeton Espinosa Bustos (1927) reported that the male flowers, at first,open quickly and with enough force to eject the pollen grains, but he does point out that later they "loose pressure" and that grains remaining in the open stamens are blown away by wind. The effective transfer of pollen from the anthers to the stigmas takes place on the surface of the water. This system appears to be efficient when observed in tanks in cultivation, but in nature fruits are very rare, and in E. potamogeton stillunknown. All species of Elodea are perennial and capable of enormous growth. They are very effectively dispersed even without specialized sporophytic diaspores. This almost aggressive vegetative growth leads to enormous competition between shoots of the same species with the consequence that one habitat becomes fully occupied by one genotype. Field observations and circumstantial evidence from herbarium studies tend to support this statement; males and females are rarely f o u n d growing intermingled. Pollen transfer on the surface of the water may well he efficient over distances best measured in centimetres, b u t for distances measured in metres or kilometres it will become inefficient or even ineffective. This is an evolutionary paradox t h a t offers an interesting project for population biologist. From a pollen tetrad all 4 grains are capable of germinating. In nature only the grains in contact with the stigma develop pollen tubes so one rarely sees more than 3 grains in a tetrad germinating. The ovary has relatively few ovules and once t h e y are fertilized the supernumerary pollen tubes develop

119 into characteristic globose or pear-shaped swellings, called cystoids by Wylie (1904), in the lumen of the ovary. CHROMOSOME

NUMBERS

The chromosome-number information published on Elodea is presented in Table I. We suspect that several early counts were incorrectly determined; Wylie (1904) and Santo ~ (1924) were almost certainly investigating E. nuttallii and not E. canadeltsis as they have reported, but lack of voucher specimens prevents a solution to this problem. Also we suspect some counts are inaccurate or perhaps "too accurate" as our investigations indicate some aneuploidy, a common phenomenon in the Hydrocharitaceae. We suspect the base number to be x=8 and not x=12 as suggested by LSve and LSve (1961); which means the counts of 2n=24 represent triploids and not diploids. PHYTOCHEMISTRY

Some aspects of the chemical composition of Elodea are summarised by Stephenson et al. (1980). The only comparative work of taxonomic value is that of Mues (1983). He examined flavonoid patterns of 37 populations of E. canadensis and 55 of E. nuttalIii from N. America and Europe, and 5 of E. caUitrichoides (named E. ernstae) from Europe. In E. canadensis and E. nuttallii native N. American and introduced material from Europe showed the same pattern. In E. nuttallii, at least males and females were alike. The flavonoid pattern was qualitatively alike in dried and fresh plants at all seasons. Elodea canadensis has apigenin, luteolin and chrysoeriol 7-0~iiglucuronides, E. nuttallii has apigenin and luteolin 7-0-diglucuronides (chryseriol 7-0-diglucuronide was lacking or present in almost undetectable quantities) and E. caUitrichoides has apigenin and luteolin 7-0-monoglucuronides. Voucher specimens of these 97 plants are in Peter Wolff's private herbarium and have been seen by us. GENETICS Sexuality

In 1910, Strasburger was trying to discover the genetic basis of sexuality in flowering plants. He had noted that E. nuttallii (called E. canadensis in his 1910 publication) had pollen in tetrads and noting that the grains germinated independantly, he postulated that 2 should give female offspring and the remaining pair should give males. Unfortunately, he died in 1912 before his experiments were finished. Winge (1923) credited Santos with the first discovery of heteromorphic sex chromosomes in flowering plants. However, Santos (1923) had "dis,

2n = 24

COLO or W I N

None None None None None ? ? KRA ? KRA ? KRA ? KRA ? KRA SLO

? Europe Origin u n k n o w n Origin u n k n o w n Origin u n k n o w n Origin u n k n o w n ? Sweden P o l a n d : S z a r S w near C r a c o w P o l a n d : Plasz6w n e a r C r a c o w Poland: Szczekocin near Cz~stochowa Poland: Strazbw near Rzesz6w Poland: Goczarkowice C z e c h o s l o v a k i a : Slovakia, Devfuska K o b y l a , Nov~ Ml~ka, Fer~houa s.n. C a n a d a : M a n i t o b a , nr. R e y k a v f k , L~ue and LSve 3013

2 n = 48 n=24d 2n = 48 d 2 n = 48 9 2n = 24 2 n = 24 2 n ffi 48 2n = 48 2n = 48 2 n ffi 48 2n = 48 2n ffi 48

None None None

? Europe ? Europe ? England

Elodea canadensis 2 n = 48 9 2 n = 48 2n = 24

Voucher

None ? STR

Locality

Elodea callitrichoides 2n = 16 ? Origin u n k n o w n 2n = 48 9 F r a n c e : B a s - R h i n , S t r a s b o u r g , Y. Sell

Gender and number

List o f c h r o m o s o m e c o u n t s

TABLE I

None

None + + + None None None None None None None None

None None None

+ +

Ill.

L~ve ( 1 9 8 1 )

Winge ( 1 9 2 3 ) Rohweder ( 1937 ) H e p p e l l in D a r l i n g t o n and Janaki-Ammal (1945) Delay (1947) Harada (1956) Harada (1956) Harada (1956) L6ve a n d L~ve ( 1 9 6 1 ) LSvekviat in W e i m a r k ( 1 9 6 3 ) WicsIo in SkaYinska e t al. ( 1 9 7 1 ) WicsIo in S k a / i n s k a e t al. ( 1 9 7 1 ) Wiczlo in Ska]tinska e t al. ( 1 9 7 1 ) Wiszlo in S k a l i n s k a e t al. ( 1 9 7 1 ) Wicslo in S k a I i n s k a e t al. ( 1 9 7 1 ) Uhrfkov~ and Fer~kov$ (1980)

Heitz (1927) Sell ( 1 9 6 7 )

Reference

Elodea nuttallii 9 × E. canadensis d 2n = 48 E. nuttallii 9 U.S.A. : Wolf L a k e n e a r Chicago. E. canadensis d C a n a d a : St. L a w r e n c e R i v e r n e a r M o n t r e a l

None

ALTA

C a n a d a : A l b e r t a , L a k e W a b a m u n , D. Allen s.n.

Elodea b ifoliata 2n = 24

None

Z

None

None None None None

None

Z

Z Z Z Z

+

? KRA

T h e N e t h e r l a n d s : K r o m m e R a a d e , nr. K o r t e n h o e f , west of Hilversum, Ketner U n k n o w n b u t p r o b a b l y U.S.A. : I n d i a n a , Wolf L a k e - s a m e m a t e r i a l as used b y S a n t o s , S t r a s b u r g e r a n d E r n s t Schwarzenbach S w i t z e r l a n d : ZUrichsee, n e a r Meilen, C.D.K. C o o k

None + + + None +

None None

None None None None None ?

Z Z

USA U S A : I n d i a n a , Wolf L a k e , 14 m i l e s f r o m C h i c a g o U S A : I n d i a n a , Wolf L a k e , 14 miles f r o m C h i c a g o U S A : I n d i a n a , W o l f L a k e , 14 miles f r o m C h i c a g o ? Japan: Honshu, Lake Biwa

Origin u n k n o w n , cult. B o t . G a r d e n Zilrich F r a n c e : D i j o n , cult. Bot. G a r d e n Zilrich

P r o b a b l e E. nuttallii b u t h a s n o t f l o w e r e d 2n = 48 E n g l a n d : C u m b r i a , B r a s s e n t h w a i t W a t e r , C.D.K. C o o k 2n = 56 F r a n c e : St. A m a n d - l e s - E a u x , J.-L. M$riaux 2 n = ca. 56 F r a n c e : Wasnes-au-Bac, J.-L. M$riaux 2 n = 48 F r a n c e : E t a n g d e T r i t h , J.-L. M$riaux

2n = 44--56 9

2n = 3 2 , 4 2 - - 4 4 d

2n = 48

Elodea nuttallii n=ca. 12d n=24d 2n ffi 48 d 2n = 48 9 2n = 48 2n = 48

2n = 48 9 2 n = 48 9

L~nd, L~t~nd, L~Snd, LiiSnd,

1st 1st 1st 1st

report report report report

Ernst-Schwarzenbach (1945b)

Packer and Witkus (1982)

R. R. R. R.

R. L ~ n d , Ist report

R. Li~Snd, 1st r e p o r t

Wylie ( 1 9 0 4 ) Santos (1924) Santos (1924) Santos (1924) L~ve a n d L~ve ( 1 9 6 1 ) K u r i t a in I k u s i m a a n d K a b a y a (1965) Czapik (1978)

R. L i i ~ n d , 1st r e p o r t R . L ~ S n d , 1st r e p o r t

122 covered" sex chromosomes in male Egeria densa Planchon and not in E. canadensis as Winge (1923) reported. In 1924, Santos reported sex chromosomes in Elodea. Santos (1923, 1924) called the plant E. canadensis, but it is clearly E. nuttallii from his description; the material that he used was collected from Wolf Lake, Indiana, U.S.A., where there are several existant herbarium collections that are clearly E. nuttallii in spite of the fact that St. John {1965) identified the material as E. canadensis. The material that Stra~ burger (1910) used for his experiments in Bonn, Germany also came from Wolf Lake and it is interesting that Strasburger's material was used 21 years later in Ziirich, Switzerland by Ernst-Schwarzenbach (1945a,b), who called it E. occidentalis, and another 38 years later by us. This Wolf-Lake strain of E. nuttallii has now been in cultivation for at least 73 years. Santos (1924) determined its chromosome number as 2n=48; the same plant today apparently has ramets showing 2n=32, 42 and 44 (Table I). Since the publications of Santos (1923, 1924) no investigations have succeeded, in spite of diligent search, in seeing these supposed sex chromosomes. It is highly unlikely that Elodea and Egeria have heteromorphic sex chromosomes. The mechanism of sex determination in dioecious flowering plants has been reviewed by Westergaard {1958 ) and additional work reviewed by Bawa (1980). Westergaard (1958) concludes his review by saying "it seems possible to recognise among dioecious plant species a series of types, which represent different degrees of remoteness from the bisexual ancestors, and which thus show different stages in the evolution from bisexuality towards dioecism". Species that are closely related to bisexual species tend to show less stability in the control of unisexuality in individual flowers. The family Hydrocharitaceae has 17 genera and of these only 7 are exclusively dioecious (3 of which are monotypic) while 5 genera have taxa with bisexual flowers (only the monotypic genus Apalanthe has exclusively bisexual flowers). The genera Halophila, Hydrilla, Ottelia and Blyxa have both monoecious and dioecious taxa while Hydrocharis, Limnobiurn and perhaps Maidenia are apparently exclusively monoecious (with unisexual flowers). From this evidence alone it can be seen that the family Hydrocharitaceae, taken as a whole, has considerable flexibility in sexual expression. The genus Elodea is not, in an evolutionary sense, remote from bisexual relations; the closest patristic relative is probably Apalanthe, a genus with exclusively bisexual flowers. Therefore, it is not surprising that the genus Elodea shows occasional 'reversions' from unisexual to bisexual flowers. Freeman et al. (1980) have reviewed the subject of change of sex in plants. Although this review is largely concerned with the factors controlling the reversal of sex in unisexual flowers, many cases are documented of plants that usually have unisexual flowers but which sometimes develop bisexual ones, these are termed subdioecious. Among subdioecious plants, according to Westergaard (1958), it is commoner for normally male flowers to become bisexual (subandroecious), but there are cases of females becoming bi-

123 sexual (subgynoecious). In Elodea the male flower is somewhat specialised for pollination at the water surface with a stamina] column and consequently the pistillodia are rarely well-developed; in the female flower all species have well-developed staminodia and occasionally these staminodia m a y develop pollen bearing anthers. A similar t~end is seen in Stratiotes according to Cook and Urrni-KSnig (1983). Freeman et al. (1980) d o c u m e n t several cases where the sexual state of individuals has changed with age, injury and disease or similarly b y the effect o f physical and chemical characteristics of the environment. Gall-like growths are associated with the bisexual flowers o f E. schweinitzii (see p. 150). We feel it likely that genetic imbalance m a y also lead to instability of sexual expression. In the related genus Ottelia crosses between plants with female and bisexual flowers gave offspring with exclusively bisexual flowers (Kaul, 1969). In Elodea sexual instability may well be associated with hybridity. Hy b rids Ernst-Schwarzenbach (1945b) carried out numerous crossing experiments with Elodea and o t h e r Hydrocharitaceae. The following crosses yielded no viable zygotes (female parent cited first): E. canadensis (2 different races) × Lagarosiphon muscoides Harvey (sub nomine L. capensis), E. canadensis (2 different races) × Hydrilla verticiUata (L.fil.) Royle; E. nuttallii (sub nomine E. occidentalis) × H. verticillata, E. callitrichoides X Egeria densa Planchon, E. callitrichoides X H. verticiUata, Lagarosiphon major (Ridley) Moss (sub nomineL, crispus) X E. nuttallii, H. verticillata × E. canadensis; our own attempts to cross Elodea with Egeria, Hydrilla and Lagarosiphon were also unsuccessful. In 1951 and 1953 Ernst-Schwarzenbach published the results o f investigations on the nature of incompatibility and hybrid inviability in the Hydrocharitaceae in general and in Elodea in detail. Within the genus Elodea ErnstSchwarzenbach (1945) found the cross E. caUitrichoides X E. canadensis, after 29 attempts to be unviable. However, she found that intraspeciflc crosses and crosses between E. canadensis and E. nuttallii yielded viable seed. These crosses are summarised on Table II. We have also found good fruit development in intraspecific crosses and in crosses involving E. canadensis and E. nuttallii, u n f o r t u n a t e l y the ripe seed was lost before harvesting. In her 1953 paper Ernst-Schwarzenbach reported that the progeny of E. canadensis × E. nuttallii and the reciprocal cross were fertile. She also carried out back-crosses which are summarised in Table II. Unfortunately, voucher specimens of her synthetic hybrids do not seem to have been kept and very little is k n o w n about the morphology o f these hybrids. In her paper there are photographs of sterile shoots of E. nuttallii × E. canadensis, but one can say little more than t h a t the plants fall within the range o f morphological variation found in each parent species. She also reports that the c h r o m o s o m e number, is 2n=48 which she considers to be the "normal diploid n u m b e r " .

1 2 3 4 5 6 7 8 9 10 11 12

E. canadensis E. canadensis E. canadensis E. nuttallii Cross No. 2 Cross No. 2 Cross No. 3 Cross No. 3 Cross No. 4 E. canadensis E. nuttallii E. canadensis

Montreal

s. loc.

Rilmlang R~imlang Montreal

Female parent

List o f Elodea crosses

T A B L E II

E. E. E. E. E. E. E. E. E. E. E. E.

canadensis nuttallii nuttallii canadensis nuttallii canadensis nuttallii canadensis canadensis canadensis nuttallii canadensis

Male p a r e n t

Montreal

Montreal Montreal s. loc.

Montreal

Montreal

Montreal

50 130 62 44 21 23 22 9 1 67 39 ?

Pollinations

9 13 37 35 10 7 5 6 1 > 34 18 ?

Fruits

12 17 62 85 16 14 6 17 3 49 ( 2 7 ) 23 26

Seeds

? 12 54 56 7 7 3 Nil Nil (19) ? 18

Seedlings

? 19 19 3d 3 9 39+3 5 Nil Nil Nil ? ? ?

Mature plants

18% 10% 59.7% 79.5% 47.6% 30.4% 22.7% 66.7% 100% >50% 46.2% ?

F r u i t set

125 F r o m our herbarium studies of North American Elodea, we believe there are naturally occurring hybrids between E. canadensis and E. nuttallii. KEY 1 (based on vegetative characteristics) Plants of all species, when grown under conditions leading to stress, tend to have pale-green, narrow (1.5 mm or less wide), parallel-sided, flat and spreading leaves; we have n o t found any reliable diagnostic features for these plants. This key is written for healthy robust plants. The largest leaves are usually f o u n d towards the shoot apex, the smallest are at the base o f stems or branches; the measurements in this k e y refer to "large" leaves. 1A. Majority o f leaves on each stem 1.75 mm wide or more 2A. Towards the stem apex leaves usually imbricate in regular rows and lying along the stem, often oblong or ovate; {anthers rarely exceeding 3 m m long} 3. E. canadensis 2B. Towards the stem apex leaves usually n o t imbricate somewhat irregular and spreading, usually lanceolate or elliptic to linear; {anthers at least in centre of flower 4 mm or more long) 3A. Usually some nodes with leaves in fours, leaves usually lanceolate to elliptic, rarely parallel-sided, at apex usually widely acute to obtuse 1. E. potamogeton 3B. Usually some nodes with leaves in pairs, never in fours; leaves usually linear and mostly parallel-sided, at apex acute 5. E. bifoliata lB. Very few leaves on a stem exceeding 1.75 mm wide. 4A. Leaves usually folded along the midrib, somewhat recurved with undulate margins, rarely more than 10 m m long 4. E. nuttallii 4B. Leaves usually flat, spreading with straight margins, at least some usually exceeding 10 mm long 2. E. callitrichoides KEY 2

(based on male flowers)

1A. Male spathes not more than 4.0 mm long, subglobose to subovoid, opening almost to base; male flowers subsessile with pedicel n o t exceeding 0.5 mm 4. E. nuttallii lB. Male spathes more than 6.0 mm long, elongate and cylindrical below, opening b y short apical slits; male flowers stalked with pedicel at least 15.0 mm long b u t usually m u c h more 2A. Pollen mostly liberated in tetmds; pedicels detaching before or during anthesis 3. E. Canadensis

126 2B.

KEY

3

Pollen liberated as single grains; pedicels remaining a short time after anthesis 3A. Leaves mostly less than 2.0 m m wide; spathe sinus rarely more than 3 m m deep; sepals lessthan 2.0 m m wide 2. E. callitrichoides 3B. Leaves mostly more than 2.0 m m wide; spathe sinus usually more than 3 m m deep; sepals usually more than 2 m m wide 4A. Leaves often paired; sepals rarely exceeding 5.3 m m long 5. E. bifoliata 4B. Leaves rarely paired, usually in threes or fours; sepals exceeding 5.3 m m long 1. E. p o t a m o g e t o n (based on female flowers)

1A. Styles very rarely exceeding 2.0 m m 2.0 m m long

long; sepals rarely exceeding

4. E. nuttallii lB. Styles usually more than 2.0 m m long; sepals more than 2.3 m m long 2A. Styles usually bifid for less than half their length, scarcely longer than the sepals 3A. Leaves linear, parallel-sided,often paired; sepals rarely exceeding 2.5 m m long; petals not exceeding 1.0 m m wide; seeds up to 4.0 m m long, densely hairy 5. E. bifoliata 3B. Leaves usually oblong to ovate, rarely paired, usually in threes; sepals usually more than 2.5 m m long; petals usually more than 1.0 m m wide; seeds up to 7.5 m m long, !sparsely hairy or glabrous 3. E. canadensis 2B. Styles usually bifid for more than half their length, much longer than the sepals • 4A. Leaves mostly less than 2.0 m m wide; styles more or less twice as long as the sepals 2. E. callitrichoides 4B. Leaves mostly more than 2.0 m m wide; styles m u c h less than twice as long as sepals 1. E. p o t a m o g e t o n

1. Elodea potamogeton (Bertero) Espinosa, Revista Chilena Hist. Nat. (Valparaiso), 31:150, dated 1927, published 19287 (spelt Helodea) - Diplandra p o t a m o g e t o n Bertero, Mercurio Chileno, 13:612. 1829 ----Anacharis p o t a m o g e t o n (Bertero) Marie-Victorin, Contrib. Lab. Bot., Univ.

127

Montrfial, 18:41. 1930. Type: Chile, "en las aguas clams de las acequias de la Quinta, Corcolen y Taguatagua, Bertero (lectotype: TO n.y.; isoand syntypes BM, G, GH, P, TO n.y.). = Anacharis m a t t h e w s i i J.E. Planchon, Ann. Mag. Nat. Hist., ser. 2, 1:86. February 1848 - Egeria m a t t h e w s i i (Planchon) Bentham and Hooker, Gen. Plant., 3(2): 1883, pro syn. = Elodea m a t t h e w s i i (Planchon)St. John, Darwiniana, 12 ( 2 ) 307. 1961. Type: Peru "ditione Ubuamantanga, prov. Canta. In aqua fluente rivulorum", April 1831, M a t t h e w s 581 (holotype: K). = Anacharis chilensis J.E. Planchon, Ann. Mag. Nat. Hist., ser. 2, 1:86. February 1848 = Elodea chilensis (Planchon) Caspary, Monatsber. KSnigl. Preuss. Akad. Wissenschaften, 1857: 47. 1857 (in reprint: Consp. Syst. Hydrillearum, p. 11. 1857) - Egeria chilensis (Planchon) Bentham and Hooker, Gen. Plant. 3(2): 450. 1883, pro syn. Type: Chile, "prope Valparaiso", 1831 (in BM 1832), Cuming 636 (holotype: K; isotype: BM). = Elodea peruviensis St. John, Caldasia (Bogota), 9(42):103, 21 December 1964. Type: Peru, Juliaca, alt. 12 550 ft (ca. 4180 m), 16 May 1902,R.S. Williams 2 5 1 6 (holotype: NY; isotypes: K,BM). = Elodea titicacana St. John,Caldasia (Bogota), 9(42):111.21 December 1964. Type: Bolivia, "vic. La Paz, Lake Titicaca, 13000 ped. (ca. 4300 m), 1890, M. Bang 165 (holotype: PH n.y., isotypes: CAN, CU, F n.v., G, GH, K, L n.y., M n.v., MO, NY, P n.y., US, Z, ZT). -- Luchia berteroniana Steudel, Nomencl. Bot., ed. 2 , 2 : 7 5 . 1841, nomen nudum. - - E l o d e a chinensis Caspary ex Index Kewensis, Suppl. 1: 152, 1901-1906, a misprint for E. chilensis. Prophylls 1.0--4.0 m m long; 1.4--3.4 mm wide at the base. Foliage leaves lanceolate, linear or narrowly elliptic to rarely ovate or elliptic, widely acute to obtuse, 4--23 m m long, 0.6--4.8 m m wide (Fig. 2a). Squamulae intravaginales ovate to widely ovate, 0.37--0.43 m m long, 0.18--0.27 m m wide. Unisexual flowers: male spathes at or after anthesis 12.5--27 mm long, cylindrical below and inflated apically (3.0--4.5 m m diam.); apical sinus 3.7--5.9 m m long, both lobes apiculate (Fig. 2e). Pedicels up to ca. 12 cm long and ca. 0.7 m m diam., flaccid, white. Male sepals 5.3--6.5 m m long, 2.0--2.8 mm wide. Male petals narrowly oblong or oblanceolate, 4.5--7.2 m m long, 0.8--2.0 m m wide. Stamens usually 7--9 fertile, 0 - 2 sterile or partly sterile; the inner 3 filaments united below into a column up to 1.2 mm long (Fig. 2f); anthers 3--4.3 m m long; pollen grains single (Fig. lf), 118--150/am diam. Female spathes cylindrical, very slightly widened above, 10--30.4 mm long, 0.6--1.2 m m diam. below, 1--3 mm diam. below the apex; apical sinus 1.5--4 m m long (Fig. 2c). Hypanthium up to 190 m m long, 0 . 3 - 0 . 6 m m wide. Female sepals 1.9--4.4 m m long, 1--1.7 mm wide.

128

Female petals 2--4.2 mm long, 0.8--2 mm wide, o f t e n cuneate at base, white or with a violet apex. Staminodia 0.3--2.2 mm long. Styles linear, bifid for 1/2--9/10 their length (2.5--) 4.5 + 1 (--6.8) m m long (Fig. 2b). Fruit ( k n o w n from one unripe specimen) at least 8 mm long, 2.8 m m wide with a ca. 5 mm long beak (Fig. 2h). Seeds when unripe at least 4 mm long. Bisexual flowers: sepals like those o f male flowers; ca. 4 mm long, 1.5 mm wide. Petals like those of male flowers, ca. 4 mm long, 1.2 mm wide. Stamens 3, antesepalous; anthers 2.8--3.2 mm long. Styles 3, antepetalous, up t o 6 m m long, bifid for at least 1/3 of the total length (Fig. 2g).

I

el ,

Fig. 2. Elodea potamogeton: (a) portion of leafy stem (scale bar: 1 cm); (b) a turion (scale bar: 1 cm); (c) female spathe (scale bar: 5 mm); (d) female flower (scale bar: 2 mm); (e) male spathe (scale bar: 2 mm); (f) male flower (scale bar: 2 mm);(g) bisexual flower (scale bar: 2 mm); (h) young fruit. Origin of material: (a) Peru, Lake Titicaca, Tutin 1101 (BM); (b) Peru, Calca, Vargas 4911 (BM); (c, d) Bolivia, La Paz, Beck (cult. Znrich); (e,f) Peru, Puno, Iltis and Ugent I443 (S); (g) Chile, Santiago, Phillippi s.n. (BAF); (h) Peru, Juliaca, Williams 2516 (K). DIAGNOSTIC FEATURES

Leaves mostly m o r e than 1.75 mm wide reaching up to ca. 4.8 mm wide, lanceolate to elliptic, usually widely acute to obtuse at apex, usually flat and spreading; styles longer than, b u t n o t twice as long as sepals and bifid for half or more than half their length; sepals of male flowers 2.0--2.8 mm wide; anthers up to ca. 4.3 mm long; pollen grains single; axillary turions develop; bisexual flowers n o t very rare.

129 DISTRIBUTION It is f o u n d in the Andes from Ecuador to Chile (Fig. 3). F r o m the equator to a b o u t 20 ° S it is f o u n d in the alpine zone mostly at an altitude of 2800-4200 m with a single specimen recorded from 4800 m. In this region it flowers almost t h r o u g h o u t the year. In Chile it is f o u n d at an altitude of 200--1000 m and mostly flowers from September to December.

~

O

o

A

Fig. 3. Distribution of: • Elodea potamogeton and * E. callitrichoides in South America. ECOLOGY E l o d e a p o t a m o g e t o n is f o u n d in lakes, reservoirs, canals, ditches and streams. It shows a preference for cool to cold, clear, oligotrophic to eutrophic, still or slowly flowing water. It is most c o m m o n in waters from 100--200 cm deep with a pH o f 8.4--9.4. The survey o f aquatic vegetation in the region o f La Paz by RamLrez and Beck (1981) gives some general ecological information, while t h e work of Collot (1980) gives detailed i n f o r m a t i o n o n E. p o t a r n o g e t o n in Lake T i t i c a c a particularly in Lake Huifiaimarca (le petit Lac Titicaca or Lac Wifiaymarca)and the bay o f Puno. In Lake Titicaca

130 E. potamogeton occupies 2 zones between the littoral Hydrocotyle--Lilaeops/s zone and the deep water zones (exceeding 4.50 m deep) dominated by Chara and Potamogeton. The first zone occupies water between 20 and 250 cm deep and consists of a mixture of E. potamogeton and Myriophyllum elatinoides Gaud. This zone is usually so dense that navigation is practically impossible. The total standing crop or biomass in this zone when undisturbed is about the same for both species; however, the production following cutting is very different, Elodea produces up to 10 g dry wt./m -2/day while Myriophyllum reaches no more than 2 g dry wt./m-2/day. Elodea has a net production of 6.34--11.26 mg O2/g dry wt./h, the maximum production is reached in February and March. In Lake Huifiaimarca, for example, E. potamogeton alone occupies about 222 km 2 which is about 16% of the surface of the lake, this represents a standing crop of 52 200 tonnes dry wt. In Bolivia E. potamogeton is readily eaten by cattle and around Lake Titicaca it is very important as fodder. To date it is not managed for extracting maximum yields; the chemical composition is given by Collot (1980). Elodea potamogeton is also found in the "Totora" zone which covers about 39% of the surface of Lake Huifalmarca; this zone is dominated by Scirpus californicus (C.A. Meyer) Steudel (= Schoenoplectus tatora (Palla) Knuth) and occupies water 2.50--4.50 m or rarely up to 6 m deep.

2. Elodea callitrichoides (L.C.M. Richard) Caspary, Monatsber. KSnigl. Preuss. Akad. Wissenschaften, 1857: 47. 1857 (in reprint: Consp. Syst. Hydrillearum, p. 11. 1857) = Anacharis callitrichoides L.C.M. Richard, Mdm. Classe Sci. Math. Phys. Inst. Imp. France, 1811 (2): 7, 75, pl. 2, bottom, dated 1812 published 1814. Type: Uruguay, "hab. circa Montevideo" Commerson (holotype: P~U n.y.; isotype G). St. John (1963) on p. 643 incorrectly designated material collected by Commerson from Buenos Aires, Argentina (P) as holotype and material collected from "Bonaria" (BM) was incorrectly designated isotype. = Elodea ernstae St. John, Darwiniana, 12 (4): 644. 1963. Type: "Argentina, Barracas al Sur (sic!), Buenos Aires, prov. de Buenos Aires, Setiembra 6, 1902, S. Venturi 1 75". St. John, p. 648 wrote that the holotype is in "S" (Stockholm), no suitable specimen has been found in Stockholm and is unlikely to have been there; St. John (personal communication, 1983) is today unsure where the holotype is to be found, we have seen specimens of "Venturi 175" in BAF (3 males)and CORD (1 male); the female element is based on material in Ziirich (Z and ZT); however, there is a discrepancy between St. John's latin diagnosis "hypanthii ad 11 cm longam" and the English description which says "hypanthium 20--28 mm long". = Elodea richardii St. John, Darwiniana, 12(4) : 649. 1963. Type: "Argentina, abundante en el agua, Las Palmas, Terr. del Chaco, 'Octobre 7, 1917, P. JDrgensen 2 5 3 5 " (holotype: US; isotypes: GH, MO, SI). Elodea callitrichoides var. ernstae G. Erdtman, Pollen morphology and plant taxonomy, angiosperms, 207--208. 1952, nom. nud.

131

Prophylls (1--) 1.5--2 (--3) mm long, 0.6--1 (--1.5} m m wide a t base. Foliage leaves linear to narrowly lanceolate or narrowly triangular gradually attenuate to an acute apex, flat (not folded), spreading, 6--15 (--24) m m long, 0.8--1.5 (--2) m m wide near base (Fig. 4a). Squamulae intravaginales m o r e or less orbicular to transversely elliptic, ca. 0.2 m m long to ca. 0.4 m m wide. Male spathes at or after anthesis (12--) 16--20 m m long, cylindrical below and inflated apically and up to 3 m m diam; apical sinus ca. 2--3 m m deep, forming a gaping mouth-like orifice with both lobes bearing apical teeth (Fig. 4d,e). Pedicels up to ca. 10 cm long and ca. 0.5 m m wide, flaccid, white, bearing spine-cells, persisting a short time after anthesis. Male sepals 4.5--6.2 m m long, 1.6--2 m m wide. Male petals linear to somewhat spathulate, somewhat longer and somewhat narrower than the sepals, very thin and flimsy, whitish-translucent sometimes with a purple vein. Stamens usually 9, sometimes 6; the inner 3 filaments united below into a column (Fig. 4e); anthers 3--3.4 m m long; pollen grains single, ca. 120--180 tLm diam. (Fig. la--c). Female spathes at or after anthesis cylindrical, not widened apically and not forming a mouth-like orifice, 11--16 {--24) m m long, 0.5--1.6

J

r r f

b r

Fig. 4. Elodea callitrichoides: (a) portion of a leafy stem (scale bar: 1 cm); (b) a fruit (scale bar: 5 ram); (c) a seed (scale bar: 1 ram); (d) young male spathe (scale bar: 2 mm); (e) male flower (scale bar: 2 ram); (f) female spathe (scale bar: 5 mm); (g) female flower (scale bar 2 m m ) ; ( h ) young style with 2 starninodia (scale bar: 2 mm); (i) 2 female petals (scale bar: 2 ram); (j) 2 female sepals (scale bar: 2 ram). Origin of material: (a,f,g,h,ij) unknown, cult. in ZUrich, Ernst-Schwarzenbach s.n. (ZT); (b,c) Argentina, San Nicolfus, Burkart 15592 (ZT); (d,e) Argentina, Rio Qui~, T. Meyer 2350 (GH).

132 mm diam. near apex, apical sinus 0.7--1.8 mm long (Fig. 4f). H y p a n t h i u m up to ca. 75 mm long, 0.3--0.4 mm diam., flaccid. Female sepals 3--4 m m long, 0.7--1 mm wide (Fig. 4j). Female petals usually s o m e w h a t longer than the sepals, very thin and flimsy, deliquescent, translucent, whitish to very pale lilac, often with 1 purple vein (Fig. 4i). Staminodia 0.8--1.2 mm long (Fig. 4g,h). Styles linear, bifid for 1/2 to 9/10 their length, 5--8 mm long, clearly projecting b e y o n d the sepals and petals (Fig. 4h). Fruit ca. 11 m m long with a ca. 4.5--6 mm long apical beak (Fig. 4b). Seeds almost smooth, some hairs at base, ca. 2.7 mm long with a ca. 1.5 mm long beak (Fig. 4c). DIAGNOSTIC F E A T U R E S

Leaves 0.8--1.5 (--2.0) mm wide near base, linear to narrowly lanceolate or narrowly triangular, gradually attenuate to an acute apex, fiat and spreading; styles a b o u t twice as long as sepals and bifid for half or more their length; spathe sinus o f male flowers rarely more than 3 mm deep; sepals of male flowers usually less than 2.0 mm wide; anthers n o t exceeding ca. 3.4 mm long; pollen grains single; seeds glabrous, ca. 2.7 mm long with a ca. 1.5 mm beak; turions n o t developed. DISTRIBUTION Temperate South America from Chaco and Corrientes southeastwards to Buenos Aires extending to the Gulf San Matfas (Fig. 3). The spread of E. callitrichoides outside South America is d o c u m e n t e d by Wolff (1980) and Simpson (1984). It was first collected in 1948 in Britain and has since then been recorded in 18 populations in southern England and one in southern Wales; by 1982 Simpson (1984) reported it to be extant in only 2 of these populations. In France, it was first discovered in several places near Strasbourg in 1958, where it could not be refound 1966 and again in 1976. In Germany, it was discovered in 1964 near Stockstadt in Hessen, 1976 near Plittersdorf in Baden and 1979 near Kehl, Baden. These localities are all relatively near the Rhine and Strasbourg. We have n o t been able to confirm other records from N.W. France because we consider flowering material essential for identification. According to Wolff (1980) and Sell (personal communication, 1983) E. callitrichoides is maintaining itself around Strasbourg and Rastatt in thermally polluted water from the Rivers Rhine and Ill. Only female plants have been seen in Europe. Elodea caUitrichoides is usually considered to be an escape from aquarium cultivation; the firm, Volbert in Speyer am Rhein, were offering it for sale in 1928 and b y 1935 female plants were in cultivation in Ziirich. ECOLOGY We have f o u n d no published information on the ecology o f E. callitrichoides in S. America, where it is today apparently not c o m m o n . In Europe it persists only in thermally polluted flowing water.

133

3. Elodea canadensis Michaux, Flora Boreali-Americana, 1:20.1803 = Udora canadensis (Michaux) Nuttall, Genera North American Plants, 2:242. 1818 = Serpicula canadensis (Michaux) Eaton, Manual Botany, N. States, ed. 5, 390. September 1829 -= Anacharis canadensis (Michaux) J.E. Planchon, Ann. Mag. Nat. Hist., set. 2, 1:86. February 1848 = Philotria canadensis (Michaux) Britton, Science, set. 2, 2:5. 1895. Type: Canada, "in rivulisCanadae" (holotype: "Elodea oblongifolia, Environs de Montreal", Michaux P n.y.;isotypes: P n.y.). = Anacharis alsinastrum Babington, Ann. Mag. Nat. Hist., ser. 2, 1:83 February 1848. Type: England, Leicestershire, Market Harborough, in ponds connected with the canal at Foxton Locks, September 1847, M. Kirby (holotype: C G E n.v.) = Elodea planchonii Caspary, Monatsber. KSnigh Preuss. Akad. Wissenschaften, 1857: 47. 1857 (in reprint: Consp. Syst. Hydrillearum, p. 10. 1857) -- Philotria planchonii (Caspary) Rydberg; Bull. Torrey Bot. Club, 35:462. 1908 ==-Elodea canadensis var. planchonii (Caspary) Farwell, Amer. Midland Nat., 10:203. 1927 = Anacharis canadensis vat. planchonii (Caspary) Marie-Victorin, Contrib. Lab. Bot., Univ. Montreal, 18:40. 1931 --- A n a c h a r i s p l a n c h o n i i (Caspary) Rydberg, F1. Prairies Plains Cent. N. America, 57. 1932. Type: Canada, "Suskatshawan", D r u m m o n d s.n. (holotype: K; isotype S -- Caspary, Jahrb. Wiss. Bot. (Pringsheim), 1 : 4 6 8 . 1 8 5 8 ) = E l o d e a latifolia Caspary, Monatsber. KSnigl. Preuss. Akad. Wissenschaften, 1857: 47. 1857 (in reprint: Consp. Syst. Hydrillearum, p. 10. 1857) --- A n a c h a r i s canadensis vat. latifolia (Caspary) Sanio, Verhandl. Bot. Verein Prov. Brandenburg, 32:121. 1890 = E l o d e a canadensis vat. latifolia (Caspary) Ascherson and Graebner, Synopsis Mitteleur. Flora, 1:403. 1897. Type: North America, "Amer. Sept. P o t a m o g e t o n dens u m L." (lectotype: to be chosen in W -- Caspary, Jahrb. Wiss. Bot. (Pringsheim), 1:467. 1858 -- the material is from the same gathering as the type of E. s c h w e i n i t z i i ) . = Philotria linearis Rydberg, Bull. Torrey Bot. Club, 3 5 : 4 6 4 . 1 9 0 8 = A n a charis linearis (Rydberg) Marie-Victorin, Contrib. Lab. Bot., Univ. Montreal, 18:41. 1931 - E l o d e a linearis (Rydberg) St. John, Rhodora 67: 29. March 1965. Type: U.S.A., Tennessee, "swamps bordering on Cumberland River, vicinity of Nashville, ?Sept. 1875, A . G a t t i n g e r s.n. (holotype: NY; isotypes: DS n.v., MO, NY, US), according to Ayensu and De Filipps (1978) it is possibly extinct in the type locality. = E l o d e a ioensis Wylie, Nat. Hist. Bull., State Univ. Iowa, 6(4): 48, pl. 1--2. 1913. Type: U.S.A., Iowa, Dickinson County, East Okoboji Lake, 1911, Wylie s.n. (lectotype: NY; isolectotype: GH). = E l o d e a brandegeae St. John, Research Studies, Washington State Univ., 30(2): 25. June 1962. Type: U.S.A., California, Truckee, pools above lumber mills, July 1908, K. B r a n d e g e e s.n. (holotype: UC), according to Cronquist et al. (1977) the locus classicus has been destroyed.

l

I

Fig. 5. Elodea canadensis: (a) leafy stem (scale bar: 1 cm); (b) "turion" (scale bar: 1 cm); (c) compact bud (scale bar: 1 cm); (d) male spathe (scale bar: 2 mm); (e,f) male flowers (scale bar: 2 ram); (g) opened ovary (scale bar: 2 mm); (h) female spathe (scale bar: 2 ram); (ij,k,l) female flowers (scale bar: 2 ram); (m) fruit (scale bar: 2 ram); (n) fruit opened (scale bar: 2 ram); (o) 2 seeds (scale bar: 2 mm); (p) enlargement of apical part of seed (scale bar: 1 mm); (q) male flower with "proliferating pistillodium" (scale bar: 2 mm); (r) enlargement of proliferating pistollodium (scale bar: 1 mm). Origin of material: (a) Sweden, Norrbotten, Lule~, Svenonius (G); (b,e) Michigan, Allegan Co., Lee, W.F. Wight 73 (U.S.); (d,e) New York, Ithaca, Morong (BM); (f) New York, Ithaca, Trelease (MO); (g,h,i,j,k,1) Alabama, Huntsville, Cook (alcohol material Z); (m,n,o,p) Indiana, Terre Haute, Evermann (U.S.); (q,r) Ontario, Thunder Bay, Carlton (BM).

L

135 Elodea oblongifolia Michaux ex Caspary, Jahrb. Wiss. Bot.(Pringsheim), 1:462. 1858, nom. illeg., pro syn. E. canadensis. -Elodea iowensis Wylie, Proc. Iowa Acord. Sci. 17:82. 1910 = Philotria iowensis Wylie,loc. cit.,pro syn.; n o m e n provisorium (later published as E. ioensis Wylie). --Babingtonia pestifera Syme in Sowerby, English Botany, ed. 3, 9:83. 1869 pro syn., nom. iUeg. -- Growforevva aquatilis Topper, original publication n o t found, the name was n o t intended to be taken seriously. -- Topperaria pestifera Anon., original publication n o t found, the name was n o t intended to be taken seriously. See also E. nevadensis St. John on p. 146 and p. 149. --

Prophylls ca. 1.5--3 mm long, 0.8--2 mm wide. Foliage leaves linear to oblong or ovate (5--) 8.1 + 1.9 (--13) mm long (1.1--) 2.0 + 0.7 (--5) mm wide, usually dark green, often somewhat crisp, widely acute to obtuse or o b t u s e - acuminate at the apex, towards the stem apex often imbricate in regular rows and lying along the stem (Fig. 5c), below the stem apex usually flat and spreading or recurred (Fig. 5a); axillary or apical turions often develop (Fig. 5b). Squamulae intravaginales widely to transversely elliptic, 0.15--0.25 m m long, 0.16--0.28 mm wide. Male spathes at or after anthesis (6--) 8.2 + 1.9 (--13.5) mm long; orifice 2--3.6 mm diam. {Fig. 5d); apical sinus 2--4 mm deep; b o t h lobes acuminate. Pedicels up to 15 cm or more long, 0.3--0.5 mm diam., flaccid, becoming detached before or during anthesis. Male sepals (3--) 3.4 + 0.4 (--4.5) mm long (1.4--) 2 -+ 0.5 (--2.9) mm wide. Male petals linear or linear-triangular to narrowly elliptic, or occasionally caudate, (1.4--) 2.6 + 0.8 (--4.3) mm long (often variable within a single flower), (0.2--) 0.5 + 0.2 (--1) mm wide. Stamens (7--)9 (--18); all filaments united below into an up to 2.2 mm long column; the outer 6 anthers (1.5--) 1.9 + 0.4 (--3) mm long, the inner 3 (1.8--) 2.1 + 0.5 (--3.2) mm long(Fig. 5e,f); pollen usually liberated in tetrads, diam. of tetrad 180--200 pm, pollen grain 120--170 p m long (Fig. lh). Female spathes 8.4--17.6 mm or more long, 1--3 mm diam. at apex (Fig. 5h); apical sinus 1--3 mm deep. H y p a n t h i u m up to ca. 25 cm long, b u t usually less, 0.4--1 mm diam., flaccid, white. Female sepals 2.3--3.5 mm long, 0.9--2 mm wide. Female petals elliptic to widely elliptic, 2--3 mm long, 0.9--1.2 mm wide. Staminodia 1--2 mm long Fig. 5i--1). Styles linear, entire or up to 1/4 bifid, 2.6--4 mm long (Fig. 5i--1), not projecting b e y o n d the sepals (usually curved between them). Ovary 1.2--1.6 mm diam. (Fig. 5g). Fruit obturbinate, 5--6.5 mm long, 2--2.5 mm diam., with a ca. 5---6 mm long beak (Fig. 5m,n). Seeds mostly basal, fusiform, ca. 4--5.7 mm long, ca. 1 mm diam. (Fig. 5o), at apex attenuate into a short beak, base o f beak with a collar o f wart-like cells {Fig. 5p).

136 DIAGNOSTIC F E A T U R E S

Leaves usually exceeding 1.5 mm wide reaching up to ca. 5.0 m m wide, usually oblong to ovate, widely acute to obtuse or obtuse-acuminate, towards the stem apex often imbricate in regular rows and lying along the stem, below the apex fiat, spreading or recurved; styles scarcely exceeding the sepals, 2.6--4.0 mm long, entire or up to 1/4 bifid; sepals of male flowers 1.4--2.9 m m wide; anthers up to 3.2 mm long; pollen grains m o s t l y in tetrads; axillary or apical turions develop; seeds glabrous with a collar of wart-like cells below the beak. DISTRIBUTION

Elodea canadensis is native in temperate North America. Figure 6 represents the distribution of flowering plant material seen b y us; we are sure each record is correct, b u t the total range is somewhat wider than that represented on our map: for example it is relatively c o m m o n on the Pacific west coast where it apparently rarely flowers. It is widespread in N. America, b u t is absent from the higher lying land (Appalachians, R o c k y Mountains and Colorado Plateau). In the north it extends up to a b o u t 55°N in Saskatchewan and southwards to about 35°N in northern Alabama. However, it seems to be concentrated around the St. Lawrence Valley and around the Great Lakes.

O O

,, t t

Fig. 6. Elodea canadensis; distribution of flowering plants in North America. Horizontal ellipses: female. Vertical ellipses: male.

137 The spread and establishment of E. canadensis in Europe is the subject of many publications, a good early summary is that o f Horn (1872) and a good later one is that of Sculthorpe (1967) or for the British Isles the work o f Simpson (1984). The "standard" story presented b y Sir J o h n H o o k e r and accepted by St. J o h n (1920) and others states that E. canadensis was first discovered in 1836 b y a gardener, J o h n New, in a p o n d near Waringstown o f C o u n t y D o w n in Northern Ireland. In 1842 it was f o u n d in a lake in the grounds of Duns Castle in Berwickshire, Scotland; the discoverer Dr. George J o h n s t o n sent material to Charles Babington, Professor o f B o t a n y at Cambridge. The discovery was lost sight of until 1847 when E. canadensis turned up simultaneously in England in reservoirs adjoining F o x t o n Locks on the canal near Market Harborough in Leicestershire, in the River Lene near Nottingham in Nottinghamshire, at Watford Locks in Northamptonshire, at Leigh Park in Hampshire and in Ireland at B o o t e r s t o w n near Dublin. F r o m about 1850 onwards it spread rapidly in the British Isles and became a serious pest b y blocking or choking waterways. By 1885 according to Siddall (1885) it had started to decline in some parts of Britain and by 1909 according to Walker (1912) it was, in most of the country, no longer regarded to be a serious pest. In the early days of its spread a great deal was published, often in local newspapers, and E. canadensis had some amusing names, for instance the Reverend Rivers T o p p e r called it "Growforevva aquatilis" but, as he encouraged it, it was soon k n o w n as "Topperaria pestifera. Professor Babington gave it in 1848 the serious botanical name Anacharis alsinastrum believing it to be a British native, b u t later agreed that it was identical to the North American species Elodea canadensis. Babington was responsible for the establishment o f it around Cambridge where it clearly escaped from the university botanic garden; it was consequently often called Bab ingtonia pestifera. Without any evidence, E. canadensis is usually considered to have been introduced into E u r o p e as an aquarium plant. We have found no evidence o f much trade of aquarium plants with North America at or before 1836. At a b o u t this time there is evidence that Aponogeton distachyos L.f. arrived in the British Isles from South Africa so there is some evidence, at least, of interest in cultivation of aquatic plants. With regard to the introduction o f t. E. canadensis we tend to support t h e t h e o r y forwarded b y Marshall (1852) w h o wrote an excellent account o f the early spread o f Elodea in Britain. Although plants collected from F o x t o n L o c k s in Leicestershire w e r e first preserved in 1847 the lock keeper stated the reservoirs there had been "full of it more than t w e n t y years back". This w o u l d mean that in the 1820's E. canadensis was already near the centre and highest point of the British canal system. It would be hard to find a single, better place to inoculate the British Isles than here. Marshall (1852) suggested that the plant was introduced with American timber that was being imported at that time for t h e construction of the railways in Leicestershire. Marshall also pointed o u t that the timber in North

138 America is floated in rafts down rivers; one seed or one fragment needed to retain its vitality in some moist cranny until it reached its destination in Britain. Douglas (1880) stated without further information that Professor Oliver said it was in Britain by 1817; we have not been able to substantiate this statement. Water currents and birds were probably responsible for the local spread of E. canadensis in Europe, but it seems that botanists and botanic gardens were largely responsible for the dispersal over long distances. For example, it is documented that Dr. E.T. Bennett sent material from England to Berlin botanic garden in 1852; in 1858 Professor Scheidweiler had it in cultivation in Ledeberg and it was in the Potsdam botanic garden in the late 1850's, in Hamburg botanic garden in 1860, and in the Leipzig botanic garden by 1861. It is fairly certain botanists inoculated continental Europe with E. canadensis; the spread within Europe is documented by Suessenguth in Hegi (1936). In Europe all the E. canadensis found to date has been female with one exception. Douglas (1880) found male plants in a pond on the Braid Hills near Edinburgh in 1879 which were again described in 1883 by Kinnear and according to herbarium material in Edinburgh (E) it persisted until 1903. The introduction of E. canadensis in Australia is unfortunately not welldocumented, but probably took place in at least 2 phases. In mainland Australia (New South Wales and Victoria) only male plants have been found while elsewhere only females are reported. The first record from Australia according to Aston (1973) dates from 1931 in Victoria, but the earliest specimen dates from Sandalong near Mildura in 1949. In New South Wales it was first recognised in 1958 in the Berriquin Irrigation District and according to Sainty and Jacobs (1981) had spread into the Murrumbidgee Irrigation Area by 1973. Elodea canadensis has become in the last 20 years the most obstructive and persistent of all aquatic plants infesting irrigation supply and drainage channels in temperate southeast Australia. Each year up to 1500 km of channels in New South Wales, infested with E. canadensis, are chemically treated. Bowmer et al. (1984) briefly described its biology in Australia and discussed control methods. In New Zealand it has also become a widespread and troublesome pest in the last 20 years, but receives less publicity because it is less aggressive than its relatives Egeria densa Planchon and Lagarosiphon major (Ridley) Moss. According to Healy and Edgar (1980) it was first recorded in 1872, but the earliest collection dates from 1916. In New Zealand only female plants were recorded until about 15--20 years ago, when males were also found; the males are now becoming more widespread than the females (I. Johnstone, personal communication, 1984). After an initial rapid spread in a new area it seems to decline in vigour and is often replaced by other invading aquatic species. In New Zealand it sometimes grows to a depth of 8.5 m where it apparently persists without competition from other aquatic macrophytes.

139 ECOLOGY Stephenson et al. (1980) have reviewed the environmental requirements of Elodea, b u t have unfortunately included work done on Egeria densa Planchon and species of Elodea other than E. canadensis in their account. The following account is based on observations on E. canadensis alone. Elodea canadensis is found in inland lakes, ponds and in slow moving water in rivers, canals and streams; it is sometimes found in slightly brackish coastal waters, b u t does n o t tolerate salinities exceeding 3.5 ppt. It prefers eutrophic calcareous water (pH 6.5--10) and cool conditions, o p t i m u m water temperature is 10--25°C. It often builds large single species stands and may be dominant in water 0.1--1.5 m deep, it has been recorded in water 12 m deep in the U.S.A. and 10.5 m deep in Norway. Its dense growth provides a habitat for different organisms, b u t the reduced temperature and oxygen concentrations within stands may be limiting for many species; mosquito larvae survival has been reported to be reduced b y 29--34% in the presence of E. canadensis. It is eaten b y many vertebrate and invertebrate herbivores, b u t is n o t a preferred f o o d plant. The fungi Chytridium elodeae Dangeard and Varicosporium elodeae Kegel have been reported on E. canadensis. At the onset of cold weather E. canadensis dies back; it often becomes black in autumn and releases various ions, particularly, manganese into the water. The spring regrowth is from underground stems crowned by roots or winter buds (turions). There is no dormancy, growth recommences as soon as the temperature rises. Elodea canadensis is very brittle and fragments easily, b u t n o t every node is capable of rooting and developing into a new plant. For a submerged aquatic plant E. canadensis tolerates relatively high levels of light, the o p t i m u m is a b o u t 16.000 lux and the net photosynthesis reaches light saturation b e t w e e n 18.000--38.000 lux (ca. 15--30% full sunlight). The oxygen c o n s u m p t i o n is 0.2--2.8 mg O2/g dry wt./h. It is generally considered to be a C3 species. Measurements of biomass of 920--2320 kg dry wt./ha have been recorded, Boruckij (1950) reported that roots were 2.6% of the biomass, b u t we suspect that other values will be found in different situations. A production of 11.7 kg/ha/day was measured in summer in Austria, in the U.S.A. net production figures of 1.16--3.20 mg C/g dry w t . / h o u r with t h e C 14 m e t h o d or 2.23--2.97 mg C/g dry wt./hour with O2 measurements have been observed. Much work has been published on the chemical composition o f E. canadensis, which is well summarised in Stephenson et al. (1980); in natural conditions protein comprises 18--27% of the dry weight; a high figure for a submerged aquatic plant. E. canadensis has a very low fibre c o n t e n t and decomposes very quickly when it has died back. It loses 50% o f its dry weight biomass in one week and 95% in 47--57 days; this is the fastest rate yet reported for a submerged vascular plant.

140 Brown and Rattigan (1979) studied the effects of 9 soluble metal ions on photosynthetic oxygen evolution from E. canadensis; a concentration of 3 mg 1-' copper is lethal to E. canadensis after 4 weeks while E. nuttaIlii will tolerate up to 6 mg 1-' copper. Elodea canadensis apparently acts as a p u m p , taking up heavy metals from the soil and releasing them into the water. The arsenic c o n t e n t of E. canadensis in New Zealand has been estimated to be 307 mg kg-', 9400 times the ambient concentration. It is very sensitive to phenols and quinones. The nitrogen removal potential of E. canadensis in an artificial p o n d is reported to be 39.8 kg ha -1, most of which is absorbed through the foliage; for phosphorus 12.1 kg ha-' has been recorded. Only 1% of shoot-derived phosphorus is translocated to the roots while 54% of the root-derived phosphorus is translocated to the shoots. VARIATION

In Elodea canadensis and other species the size of the leaves and the number of leaf whorls per unit length of stem is very variable and can only be used for identification purposes with extreme caution. Adams et al. (1971) investigated the relationship between nutrient pollution, element constitution and variation in morphological expression in E. canadensis from 24 stations in Pennsylvania, U.S.A. Full morphological analysis of 19 morphological characters of plants from 5 sites was carried o u t and numerous correlations were obtained suggesting causal relationships b e t w e e n the concentration of certain elements and the expression of several morphological characters. In general, it was found that in response to increased levels of nutrient enrichment the leaf width declined while leaf length increased, but the number o f leaf whorls decreased per unit length of stem probably as a result of increased internodal elongation. Decreasing variability in leaf length was also correlated with decreased number o f leaf whorls. The variation described by Adams et al. (1971) is almost certainly a manifestation of phenotypic plasticity. After examining the h o l o t y p e and several isotypes o f E. linearis we are n o t able to agree that the stamens are equal in length and equally attached to the hypanthium. We consider it to be indistinguishable from male E. canadensis. N o t all the morphological variation observed in E. canadensis is likely to be due to p h e n o t y p i c plasticity. For example, outside America E. canadensis is remarkably constant in form and in Europe is very rarely to be confused with E. nuttallii or E. callitrichoides, but in North America it is often impossible to distinguish non-flowering plants o f E. canadensis and E. nuttallii. The lack o f variation in Europe is probably because very few genotypes have become established. In North America some of the variation m a y be due to hybridization (see p. 123 and p. 145) while some may be inherent to the species. For example, around the headwaters o f the Mississippi River (Itasca National Park) the plants are florally typical E. canadensis, b u t have rather

141 wide leaves -- a character that remains in cultivation -- in the Pacific Northwest the E. canadensis usually has sharper pointed leaves than elsewhere, with experience it is often possible to predict the collection location by the "look" of the plant. We have not found it possible to quantify this information because phenotypic plasticity is responsible for a much wider range of variation in nature and it is not reasonable to base a classification on plants cultivated under "standard" conditions. 4. Elodea nuttallii (J.E. Planchon) St. John, Rhodora 22:29. 1 9 2 0 - A n a charis nuttallii J.E. Planchon, Ann. Mag. Nat. Hist., ser. 2, 1:86. February 1848 = Philotria nuttallii (Planchon) Rydberg, Bull. Torrey Bot. Club, 35:461, 465. 1908. Type: U.S.A. "in America septentrionali" (holotype: "Phil.[adelphia] " s.d., T. N u t t a U s.n. BM). = E l o d e a c o l u m b i a n a St. John, Research Stud., Washington State Univ., 30 (2):37. June 1962. Type: U.S.A., Oregon, 'Columbia Bottoms', near Portland, May 1889. D r a k e and D i c k s o n (holotype: F - - sheet No. 2538789). - - S e r p i c u l a verticillata L. fil., var. angustifolia Muhlenberg, Cat. Plant. Amer. Septentr., 84. Oct. 1813, nora. nudum - E l o d e a canadensis var. angustifolia (Muhlenberg ex) Ascherson and Graebner, Synopsis Mitteleur. Flora, 1:403. Dec. 1897, pro syn. = Philotria angustifolia (Muhlenberg ex) Britton ex Rydberg, Flora Colorado, 15. 1906. - - Serpicula o c c i d e n t a l i s Pursh, F1. Amer. Septentr., 1: 33. probably Dec. 1813 --- U d o m occidentalis (Pursh) Koch, Syn. F1. Germ. Helv., ed. 1, 669. Oct. 1837 = E l o d e a o c c i d e n t a l i s (Pursh) St. John, Rhodora, 22: 27. 1920 - Philotria o c c i d e n t a l i s (Pursh) House, Bull. New York State Mus., 243---244:55. 1 9 2 3 = A n a c h a r i s o c c i d e n t a l i s (Pursh)Marie-Victorin, Contrib. Lab. Bot., Univ. Montr6al, 18:40. 1931; nora. illeg., based on E l o d e a canadensis Michaux. - - Udora verticillata (L. ill.) Sprengel, var. m i n o r Engelmann ex Caspary, Monatsber. K~nigl. Preuss. Akad. Wissenschaften, 1857:46. 1857 (in reprint: Consp. Syst. Hydrilleamm, p. 10. 1857) nom. illeg., pro syn. - Philotria m i n o r (Engelmann ex Caspary) Small, F1. Southeastern U. States, 47. Oct. 1903 - E l o d e a m i n o r (Engelmann ex Caspary) Farwell, Rep. Michigan Acad. Sci., 17: 181. 1916. Prophylls 1--2.7 mm long, 0.75--1.3 mm wide, transparent (Fig. 7b). Foliage leaves linear to lanceolate, (4--) 7.7 -+ 2.7 (--15.5) mm long (0.9--) 1.4 -+ 0.4 (--2.4) mm wide, frequently recurved with undulate margins and folded along the midrib (not regularly imbricate) (Fig. 7a), usually pale green and flaccid, at apex acuminate. Squamulae intravaginales elliptic to circular, rarely transversal elliptic, 0.17--0.44 m m long, 0.1-0.28 mm wide. Male spathes at or after anthesis subglobose to subovoid (2.2--) 3.4 -+ 0.9 (--4) mm long (1.5--) 2.1 -+ 0.5 (--3) mm wide, both lobes apiculate, opening almost to base (Fig. 7d). Pedicels up to 0.5 mm long, male flowers abscissing

142

in bud. Male sepals (1.7--) 2.2 -+ 0.2 (--2.6) m m long (1.2--) 1.6 + 0.3 (--2) m m wide (Fig. 7b). Male petals triangular to narrowly triangular or rarely linear, mostly caudate (0.5--) 1 -+ 0.4 (--1.5) m m long (often variable within a single flower) (0.2--) 0.4+ 0.2 (--0.6) m m wide (Fig. 7g). Stamens ( 7 - - ) 9 (Fig. 7h); the inner 3 filaments united below into an up to 0.5 m m long column; the outer 6 anthers (0.8--) 1.1 + 0.2 (--1.4) m m long, the inner 3 (0.9--) 1.3 + 0.4 (--1.8) m m long; pollen usually liberated in tetrads (Fig. l d ) , diam. o f tetrad 120--210 ~m, pollen grain 86--120 g m long (Fig. le). Female spathes 8.5--14.5 m m long, 0.8--1.8 m m diam. at apex (Fig. 7i); apical sinus 0.1--2.5 m m deep. H y p a n t h i u m up to ca. 25 cm long but usually less. Female sepals 1--2.1 m m long, 0.6--1.1 m m wide (Fig. 7k). Female petals elliptic to widely elliptic or obovate, 1.1--1.9 (--2.5) m m long, 0.5--1.3 m m wide (Fig. 71). Staminodia 0.5--1.2 m m long (Fig. 7m). Styles linear, entire or up to 1/3 bifid (Figs. 7j,n), 1.2--2 m m long, not projecting beyond the sepals (usually recurred between them). Ovary ca. 0.8 m m diam. Fruit obclavate, ca. 5--10 m m long, 1.5--2 m m diam., with a ca. 4--6.5 m m long beak (Fig. 7o). Seeds basal and parietal, fusiform, 4--4.6 m m long, ca. 1 m m diam., at base long hairs, the rest glabrous or bearing some hairs, at apex attenuate into a short beak w i t h o u t a collar Fig. 7p).

,

Fig. 7. Elodea nuttallii: (a)leafy stem (scale lbar: 1 cm); (b) axillary shoot (scale bar: 5 mm); (c) leaf tip (scale bar: 0.2 ram); (d) male spathe (scale bar: 2 mm); (e) male flower bud opening (scale bar: 2 ram); (f) 3 sepals (scale bar: 2mm); (g) 3 petals (scale bar: 2 ram); (h) 7 stamens (scale bar: 2 ram); (i) female spathe (scale bar: 5 mm); (j)female flower (scale bar: 2 mm); (k) 3 sepals (scale bar: 2 mm); (1) 3 petals (scale bar: 2 mm); (m) 3 staminodia (scale bar: 2 ram); (n) 3 styles -- papillae omitted (scale bar: 2 mm); (o) an opened fruit (scale bar: 5 mm); (p) 2 seeds (scale bar: 1 ram). Origin of material: (a--n) cultivated in Botanic Garden, Zilrich; (c--h) probably from Indiana, Wolf Lake; (a,b,i--n) from Z~richsee; (o,p) from Wisconsin, Hotchkiss and Koehler 4292 (U.S.).

143 DIAGNOSTIC F E A T U R E S

Male spathes at or after anthesis subglobose to subovoid, 2.2--4.0 mm long, 1.5--3.0 mm wide, opening nearly to base; leaves rarely more than 1.75 mm wide, usually folded along the midrib, usually 'recurred' and often with a somewhat undulate margin; styles not projecting beyond the sepals, 1.2--2.0 mm long, entire or up to a third bifid; male flowers subsessile becoming detached while in bud; sepals 1.2--2.0 mm wide; anthers up to 1.8 mm long; pollen grains mostly in tetrads; turions absent; seeds with short hairs at base otherwise almost glabrous and lacking an apical collar. DISTRIBUTION

Elodea nuttallii is native in temperate North America. Figure 8 is based on flowering material only. Elodea nuttallii is largely sympatric with E. canadensis and is absent from higher lying land. In contrast to E. canadensis it does not extend so far north and seems to be concentrated rather more south in the states of Illinois and Missouri or in the east along the Atlantic coast from Maine to Virginia. The spread of E. nuttallii in Europe is documented by Wolff {1980). It was first collected in 1939 in Belgium, but was not correctly identified until 1955. In 1941 it was found in The Netherlands, 1961 in East Germany,

0

0

0

A_

"°°

•""

•

°o

"

Fig. 8. Elodea nutallii: distribution of flowering plants in North America. Horizontal ellipses: female. Vertical ellipses: male.

144 1966 in Britain, in 1973 in West Germany and Switzerland, and perhaps 1977 in Austria (Lindex, 1978 -- this record has been confirmed by De Langhe, but the herbarium material distributed by the Institut ftir Botanik Graz, Nr. 274 from Lunzer See, 18 June 1981, Pittoni, has been seen by us and is E. canadensis). Generally female plants are found, but in Rodewisch, Vogtland in East Germany only male plants have been found. E. nuttallii is generally considered to have been introduced into Europe as an aquarium plant. Wolff (1980) reports that in 1953 both male and female plants were in cultivation in the botanic gardens in Mfmster. However, one must not forget that male plants, at least, were in cultivation in the botanic gardens in Bonn before 1910 for Strasburger's experiments and were in Ziirich in cultivation by 1934 for Ernst-Schwarzenbach's experiments (see p. 123). Female Elodea nuttallii is actively spreading in many parts of Europe and seems to be replacing E. canadensis in many localities. Simpson (1984) gives a thorough account of its spread in Britain; it was first discovered in 1966 near Oxford, by 1974 it was found in 6 vice-countries, by 1975 in 10 vicecountries, by 1978 in 35, by 1982 in 40. There appears to be today no decline in the number of stations; it is represented by 1 population in Ireland and 3 in Wales. Simpson (1984) wrote that it is not known in Scotland, but C.D.K. Cook found specimens in the Edinburgh herbarium collected from East Ross (Munlochy, 19 June 1978, McCaUum Webster 1940) and from Stirling (Forth-Clyde Canal, nr. Castlecary, 22 September 1983, N.F. Stewart s.n. ). The biology of E. nuttallii in Japan is well described by Kunii (1982). It was first discovered in the early 1960s (Ikusima and Kabaya, 1965) in Lake Biwa and is at the moment rapidly spreading and becoming established in many lakes, ponds and streams. Male plants only have been found in Japan. ECOLOGY

Remarkably little has been written on the ecology of E. nuttallii within its native range, but what is known is summarised by Stephenson et al. (1980). In Japan, Kunii (1982) has written an excellent and detailed account and for Europe the accounts of Weber-Oldecop (1977), and M~riaux and G~hu (1979) are useful. Elodea nutallii grows in calcareous waters in lakes, ponds, slowly flowing streams and canals, and on tidal fiats; it tolerates salinities up to 14.4 ppt (approaching half normal sea water). The seasonal changes described by Kunii (1982, 1984) match our observations made in Switzerland. From December or January to March E. nuttallii overwinters as prostrate shoots with green leaves that form dense mats on the bottom; these shoots grow when the temperature exceeds 4°C. Kunii (1981) discovered that detached portions of shoots grow faster in winter than undetached rooted parts. When the water reaches 10°C (late March in central Japan) new shoots develop from the prostrate shoots and grow rapidly upwards almost without branch-

145 ing until they approach the surface when vigorous branching takes place. These branched shoots form a dense canopy just below the surface of the water. From mid-June to November the unbranched stems connecting the canopy with the roots become defoliated and the roots die. The maximum shoot biomass (1693 g dry wt./m -2) is found in September with most biomass in the top 30-cm layer. The root biomass has a maximum in June and a minimum in September. From September onwards the branched apical shoots become detached and sink in November and December. According to Stephenson et al. (1980) the critical concentration of phosphorus for E. nuttaUii is reported to be 0.14% of the plant dry weight, of nitrogen it is 1.6% of the plant dry weight; in the laboratory growth is r e duced 35% at nitrogen concentrations of 0.03 mg 1-1. The carbonate deposits (marl) that form as a result of photosynthesis have been reported to proceed at the rate of 2 kg calcium carbonate/100 kg of plant in 10 h. According to Burk (1977) E. nuttallii has been found to be resistant to petroleum pollution surviving when all other plants are killed. VARIATION

The shape and size of the leaves are phenotypically plastic and it is sometimes not possible to distinguish luxuriant, non-flowering plants of E. nuttallii from depauperate E. canadensis, a fact documented by Lawrence (1976) from field and laboratory studies. First generation hybrids between these species would be expected to be morphologically intermediate, a point supported by the photographs published by Ernst-Schwarzenbach (1953). A serious taxonomic difficulty is that these hybrids come within the range of variability where there is phenotypic overlap between E. canadensis and E. nuttallii on vegetative characters. Ernst-Schwarzenbach {1953) reported that the hybrid E. canadensis X E. nuttallii was fertile and she made some back~crosses (see Table II). Elodea species are long-lived perennials capable of almost limitless growth as witnessed by the asexual spread of E. canadensis and E. nuttallii outside America. The combination of vegetative growth and fertile F1 hybrids should lead to the establishment of several different and perhaps widespread nothomorphs as has apparently happened in the genera Nuphar and Potamogeton. Outside America E. canadensis and E. nuttallii are remarkably constant, and it is rare to find plants that cannot be assigned to one or the other species. In North America both species are clearly more variable. These nothomorphs can only be recognised with certainty on the basis of floral characteristics, but flowers apparently rarely develop and are even more rarely collected. St. John (1962) described E. columbiana on the basis of obdeltoid and somewhat petaloid staminodia, which we have occasionally seen in E. nuttab lii throughout its range and occasionally these staminodia may even bear pollen. St. John had seen 3 female plants only; we have seen good male E. nuttallii from the region (Oregon: Columbia River, s.d., Nuttall s.n. (BM),

146 one sheet bears male and female flowers). Therefore, we consider E. colum. b/ana to be a s y n o n y m of E. nuttaUii.

5. Elodea bffoliata St. John, Research Studies, Washington State Univ., 30(2):23. June 1962. Type: U.S.A., Arizona, Coconino Co., "Com[mon] in Slough near Flagstaff", alt.,2270 m, 27 August 1923, H.C. and E.E. Hanson A 892 (holotype: MO). = E. longivaginata St. John, Research Studies, Washington State Univ., 30(2):38. June 1962. Type: Canada, Alberta, "in a lake at the northern edge of the Milk River Range, where the Lethbridge Trail leaves the summit", 20 July 1895, J. Macoun 13725 (holotype: CAN). The stigmas on the type specimen are bifid for 1/3 to 1/2 of their length and not undivided as stated in the original description, and they are longer and not shorter than the sepals. = ? E. nevadensis St. John, Research Studies, Washington State Univ., 30(2):41. June 1962. Type: U.S.A. Nevada, Washoe Co., Wadsworth, 21 July 1887, Tracy and Evans 475 (holotype: NY;iisotype: NY), according to Cronquist et al. (1977) it is extinct from the locus classicus. The flowers on the type specimen have been partially destroyed but one style appears to be more than 1/4 bifid,which indicatesE. bifoliata, but the specimen might possibly represent E. canadensis. Prophylls up to ca. 2 m m long and 1 m m wide. Foliage leaves linear to narrowly elliptic or rarely lanceolate, 4.7--24.8 m m long, 0.8--4.3 mm wide, usually pale green, flat and spreading, with straight and parallel margins, at apex widely acute; very often m a n y leaves in pairs and internodes often longer than the leaves (Fig. 9a). Squamulae intravaginales circular to oblate, 0.21--0.25 m m long, 0.2--0.27 m m wide. Male spathes at or after anthesis 10.4--42.0 m m long (St. John reported up to 150 m m long but we have not confirmed this), cylindrical below, orifice 1.5--4.5 m m diam; apical sinus 2.9--5.0 m m deep, both lobes shortly apiculate (Fig. 9b). Pedicels up to 7 cm or more long and ca. 0.6 m m diam. white, thin, flaccid, probably abscissing at or shortly before anthesis. Male sepals (2.3--) 4.2--6.1 mm long {1.2--) 1.6--2.4 mm wide. Male petals narrowly oblong or oblanceolate (2.7--) 5 . 0 - 6 . 2 m m long, 0.6--1.0 m m wide. Stamens usually (7--) 9 fertile, 0--2 sterile; the inner 3 filaments united into a column up to 1.5 mm long; anthers (1.5--) 3.0--4.5 m m long (Fig. 9c); pollen grains single (Fig. lg), 105--141 ~ m diam. Female spathes: 9 - 6 7 m m long; 1.0--1.5 m m diam. at orifice; apical sinus 1.5--2.9 m m long (Fig. 9d). Hypanthium up to 32 cm long, but usually less, 0.4--0.6 m m diam. Female sepals 1.8--2.7 m m long, 0.8--2.9 mm wide. Female petals narrowly elliptic or oblanceolate, 2.1-2.8 m m long, 0.6--1.0 m m wide. Staminodia: 0.8--1.4 m m long. Styles linear, bifid for 1/4--2/3 of their length, 2.3--3.0 m m long (Fig. 9e). Fruit mostly ovate, beaked; 6.5--8.0 m m long, 2.3--4.5 m m diam.; beak up to 20 mm long (Fig. 9g). Seeds 1--10; narrowly ellipsoidal, shortly beaked,

147

a

Fig. 9. Elodea bifoliata: (a) leafy stem (scale bar: I cm); (b) male spathe (scale bar:

5 mm); (c) male flower (scale bar: 2 mm); (d) female spathe (scale bar: 5 ram); (e) female flower (scale bar: 2 ram); (f) 2 seeds (scale bar: 2 mm);(g) fruit (scale bar: 10 ram). Origin of material: (a) Arizona, Coconino Co., Ke~ and Pinkava P13699 (NY); (b,d) Arizona, Coeonino Co., Flagstaff, Hanson and Hanson A 892 (MO); (c,e) Nevada Elko Co., Tiehm 5428 and Williams (NY); (f) Colorado, Larimer Co., State Agric. Coll. 2421 (NY).

2.~--3.0 mm long, 0.9--1.0 mm diam., densely covered in white unicellular hairs, 0.5--1.0 mm long, w i t h o u t apical collar (Fig. 9f). DIAGNOSTIC FEATURES Leaves mostly parallel-sided, linear to narrowly elliptic or lanceolate, usually exceeding 1.75 mm wide, widely acute at apex, flat, spreading, paired leaves c o m m o n ; turions probably absent; styles scarcely exceeding the sepals, 2.3--3.0 mm long, bifid for a b o u t one quarter to two-thirds of their length; sepals of male flowers 1.2--2.4 mm wide; anthers up to 4.5 mm long; pollen grains single; seeds densely covered with hairs. DISTRIBUTION E l o d e a b i f o l i a t a is native to temperate North America (Fig. 10). It is almost completely allopatric to E . c a n a d e n s i s a n d E . n u t t a l l i i occupying the higher lying land extending from southern Alberta southwards to Arizona and New Mexico; in the east from Colorado extending westwards to Nevada.

148

::" '" ~

•

•o

5o

Fig. 10. Distribution of: • Elodea bifoliata and • E. schweinitzii.

SPECIMENS EXAMINED C A N A D A . A L B E R T A : northern edge of Milk River Range, where the Lethbridge trail leaves the summit, 20 July 1895, Macoun 13725 ( C A N 9 ). SASKATCHEWAN: Maple Creek, Climax, 10 miles au sud-est Lac de l'lle,17 June 1958, Boivin and Perron 12138 (CAN 9, NY). USA. ARIZONA: Coconino Co.: Slough near Flagstaff, alt. ca. 2270m, 27 Aug. 1923, H.C. and E.E. Hanson A 8 9 2 (MO 9, d); Coconino Nat. Forest, about 8 miles south of Mormon Lake, 19 August 1970, Correll and Correll 39454 (NY d ); Pine Springs, west of Williams, 20 August 1970, Correll and CorreU 39487 (NY 9, d); 4 miles N. of Williams, 31 July 1966, Crutchfield 1874 (NY 9); 9 miles E of Williams, 27 June 1967, Crutchfield 8179 and Mitchell (NY d);: Lake Mary, 10 miles SE of Flagstaff, 28 Sept. 1965, Crutchfield 875 (NY 9, d); ibid., alt. ca. 2500 m, 2 June 1959, Demaree 41089 (ASC d); ibid., Dearer 5492 (ASC d); Lockett Meadows, N. side of San Francisco Peaks, 10 August 1976, Kiel, Reeves and Hevly P13699 (NY 9, d); ibid alt. ca. 327 m, Hevly, Kiel, Pinkava and Griffith herb. No. 30654 (ASC 9); Pickett Lake, 16 miles SE. Flagstaff, 7 October 1983, Ricketson 808 (ASC d); Navajo Co., Cooley Lake, Fort Apache, 23 August 1966, Crutchfield 2034 (NY 9). COLORADO: Latimer Co., Lee's Lake, alt. ca. 1730 m, 21 July 1896, Cowen s.n., (MO d); ibid., 24 September 1896, State Agric. Coll. 2421 (US 9); ibid., 5 August 1897, Crandall 2423 (GH d, NY d);Fort Collins, alt. ca. 1700 m, 21 July 1896, Cowen s.n. (UC 9, d); Rio Blanco Co., Stuntz Reservoir, alt. ca. 2430 m, 3 September 1982, Neese and Trent 12352 (NY d ). IDAHO: Fremont Co., SW. edge of St. Anthony, Snake River, 15 July 1949, Christ and Christ 18979 (NY 9, d; WS 9, d).

149 MONTANA: Philips Co., NE. of Loring, Reservoir 158, 30 August 1939, Hotchkiss 6348 (US 9); Toole Co., Shelby City Reservoir, 9.5 miles N. of Shelby, 25 July 1981, Taylor and Taylor 30857 (NY 9); Thibedeau Lake, Havre, 24 July 1922 or 1932, Sperry 77 (US sterile). NEVADA: Washoe Co., Wadsworth, 2 July 1887, Tracy and Evans 475 (NY 9); Truckee River, at Nixon, alt. 1310 m, 23 July 1977, Tiehm 3688 (MO 9, NY 9); Elko Co., Duck Valley, Coyote Hole, alt. ca. 173 m, 20 July 1979, Tiehm 5428 and Williams (NY 9, d); Douglas Co., 2.2 ml., N. of CenterviUe, alt. ca. 1430 m, 17 July 1977, Tiehm 3637 (NY 9); Carson River, S. of Gardnerville, alt. 1480 m, 25 July 1977, Tiehm 3715 (NY 9); Churchill Co., Harmon Res., E. of Fallon, air. 1304 m, 2 August 1977, Tiehm 3797 and Lott (MO, NY sterile). NEW MEXICO : Rio Arriba Co., Jicarilla Apache Reservation, Lake La Jara, 22 August 1911, Standley 8274 (US 9, d); ibid., 25 August 1970, CorreU and Correll 39601 (NY 9, US 9); Mora Co., Charette Lake, 15 Miles W. of Nolan, 7 October 1966, Crutchfield 2330 (NY 9); Sandoval Co., Fenton Lake, 20 October 1966, Crutchfield 2387 (NY sterile); Taos Co., Taos, 13 August 1969, Correll and Correll 37704 (NY); San Miguel Co., 10 ml. SE. Las Vegas, 11 August 1965, Crutchfield 647 (NY 9). NORTH DAKOTA : Morton Co., 7 miles E. of Bismark, 24 August 1917, Metcalf 358 (US d); Golden Valley Co., Beach, 11 August 1941, Stevens 562(US 9); Wash Co., Park River, 7 July 1944, Stevens 773 (US sterile). SOUTH DAKOTA: Charles Mix Co., Bass Pond, Lake Andes, 16 June 1926, Over 17170 (UC 9, d;US 9, d). UTAH: Wasatch Co., Strawberry Reservoir, South End, 6 August 1936, Hotchkiss 4933 (US sterile); Utah Co?, Fish Lake, hr. Twin Creeks, 25 August 1938, Bassett Maguire 16221 (UC sterile); Cache Co., mouth of Logan Canyon, 18 October 1940, Bassett Maguire 20262 (WS 9 ); ibid., 20263 (WS 9 ). WYOMING : Albany Co., Seven Mile Lakes, 7 Sept. 1961, Goodding 597 (GH d ; NY ~ ; UC ~ ); Teton Co., Two Ocean Lake, 4 August 1953, Porter 6365 (UC d); Natrona Co., 29 June 1953, Porter 6259 (NY 9, d ; UC 9, d).

NOTES T h e r e is little d o u b t t h a t E. longivaginata and E. bifoliata are conspecific. B o t h were p u b l i s h e d at the same time, b u t we have a d o p t e d E. bifoliata as t h e n a m e because St. J o h n ' s original d e s c r i p t i o n o f E. longivaginata d o e s n o t fit t h e h o l o t y p e and because t h e h o l o t y p e o f E. bifoliata is a m a l e p l a n t w i t h well-preserved f l o w e r s and m a t u r e pollen. T h e i d e n t i t y o f E. nevadensis is d o u b t f u l : St. J o h n c o n s i d e r e d t h e swollen tips o f t h e s t a m i n o d i a t o be an imp o r t a n t diagnostic f e a t u r e , b u t we have f o u n d s t a m i n o d i a w i t h swollen tips n o t t o be unusual in Elodea. A n o t h e r d i f f i c u l t y is t h a t t h e t y p e specimen o f E. nevadensis is p o o r l y c o l l e c t e d and its f l o w e r s are p a r t l y d e s t r o y e d , the f r a g m e n t o f style is divided w h i c h is in f a v o u r o f E . bifoliata, b u t it c o u l d be a s o m e w h a t a b n o r m a l E. canadensis. E l o d e a bifoliata differs f r o m all o t h e r species o f E l o d e a b y t h e p r e s e n c e o f a d e n s e i n d u m e n t u m o f hairs o n t h e seeds. T h i s species, a b o v e all o t h e r s , is

150

highly fertile, most collections have male and female plants and if collected at the right time of year have capsules containing ripe seed; in contrast, the ripe seeds of E. canadensis are very rare and those o f E. potamogeton are still unknown. We have no evidence that E. bifoliata is monoecious, b u t we suspect that it might be. We k n o w nothing o f the biology o f this species, b u t from herbarium material we suspect that it is like other species of Elodea, b u t m a y occasionally be an annual as it apparently sometimes grows in pools that m a y dry out. ATAXON OF UNKNOWNPROVENANCE

Elodea schweinitzii (J.E. Planchon) Caspary, Monatsber. K6nigl. Preuss. Akad. Wissenschaften, 1857:46. 1857 (in reprint: Consp. Syst. Hydrfllearum, p. 10. 1857) - Apalanthe schweinitzii J.E. Planchon, Ann. Mag. Nat. Hist., set. 2, 1:87. February 1848. Type: USA, "in America septentrionalis provinciis confederatis, loco proprio non indicato, Schweinitz in Herb. H o o k " . (holotype: K probably collected in Pennsylvania near Bethlehem or Nazareth -- see St. J o h n , R h o d o r a 67:3--6. 1965; iso- or syntypes: BR n.y., K,S), according to Ayensu and De Filipps (1978) it is probably extinct. SPECIMENS EXAMINED

USA: -- Pennsylvania: Bet[hlehem), 1832, Schweinitz (K); Bethlehem, s.d., Wolle (GH); Bethlehem, 1832, Moser (CAS n.y., NY, P n.y.); "in Lecha", July--August, 1932, Moser (K); "in der Lecher bei Bethlehem", July 1832, Princ Wiedensis (BR n.y.); Nazareth, s.d., Schweinitz (PH n.y.). New York: mouth of Fishkill Creek, August-September 1816, Cuevels? (NY). Old specimens without precise locality (Am. bor., Amer. sept., N. Amer. or nothing): without collector -- probably Schweinitz (K, M, PH n.y.); with collector: s.d., Schweinitz (K,S); 1829, Schweinitz (BR n.y.). The collection labelled "New Jersey, N. Caesar, 1834, Torrey" in Paris is considered by St. John (1965) to be mislabelled specimens collected from Bethlehem, Penn.

Elodea schweinitzii is something of a taxonomist's nightmare. It was first collected in 1816 in Fishkill Creek, New York (Dutchess County) where it has never been found since and then again from 1829 to 1832 in Pennsylvania (Fig. 10) in a small region around Bethlehem where it has also, in spite o f repeated searches, never been found again. In b o t h these regions it is sympatric with E. canadensis and E. nuttallii. The flowers of E. schweinitzii are bisexual, b u t it is not clearly a bisexual race of an existing species. For example, E. potamogeton occasionally develops bisexual flowers, b u t except for the presence o f styles and stamens in the same flower all other characters clearly remain like those o f E. potamogeton. In E. schweinitzii one can almost say the main characteristic is variability itself. The variability is in form and size o f almost all floral organs but it is not constant for a particular plant, or for different flowers on one plant or for different organs within a single flower.

151

The perianth has 3 sepals and 3 petals. The sepals are 1.7--2.6 m m long and 0.9--1.4 m m wide; the petals are 1.0--3.0 m m long, 0.3--1.1 m m wide and vary from oblanceolate to circular. The stamens are 2--7 (av. 3.75) in number, when there are 2 or 3 then they are antepetalous (Figs. l l d , e ) , but when m o r e then t h e y are irregularly arranged. The stamens are quite unlike those o f E. canadensis or E. nuttallii, they have elongate filaments, 0.4--0.6 m m long with ellipsoidal anthers, 0.3--0.8 m m long (Figs. l l d , e ) . . The anthers are usually bispe rangiate but occasionally unisporangiate. The pollen is shed as single grains which are usually withered, often lack an echinate exine and are probably sterile. The staminodes are linear and 0--5 (av. 1.8) in n u m b e r but the number itself is not correlated with the n u m b e r of stamens. The gynoecium shows the greatest developmental irregularities. The ovary is usually stalked (Fig. l l a ) , this is a unique feature in the genus Elodea. The styles are either simple (1.8--4.7 m m l o n g ) partly bifid or divided almost to

P

b

1I

Fig. 11. Eiodea schweinitzii: (a) a spathe with flower (scale bar: 1 cm); (b) a normal opened ovary (scale bar: 1 mm); (c) an abnormal opened ovary (scale bar: 1 mm);(d,e) flowers (scale bar: 2 mm). Origin of material: (a) "Am. bor. Muhlenberg" (S); (b,c) New York, Fishkill Creek, Cuevels? (NY); (d) Pennsylvania, Bethlehem, Moser (G); (e) ibid., (NY).

152

the base, often with branches of different lengths (Figs. l l d , e ) ; there are 4-9 stigmas, 0.5--4.2 mm long. In some ovaries there are filamentous and papillose outgrowths which appear to replace the lower ovules {Fig. l l c ) and probably represent stylodia. Ripe seeds and fruits have never been found. The leaves are 7.9--11.0 mm long and 1.0--2.8 mm wide. They usually fall within the range of E. nuttallii, but one collection of Moser (G) has leaves like E. canadensis. Some plants have swollen gynoecia and it is possible that this whole teratological development is due to an insect or mite as St. John (1965) suggested. However, this is unlikely as this schweinitzii-syndrome is so restricted in time and place. St. John's second suggestion of hybrid origin of E. schweinitzii is more acceptable and perhaps it really represents a shortlived F2 or back-crossed individual with some double recessive allele. However, it does not represent a simple F1 hybrid between E. canadensis and E. nuttallii (see p. 123). ACKNOWLEDGEMENTS

We would like to thank the Fonds National Suisse de la Recherche Scientifique (No. 3.314.78) for a part-time, post
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