Two new species of seagrasses from Australia, Posidonia sinuosa and P. angustifolia (posidoniaceae)

Aquatic Botany, 6 (1979) 307--328

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© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

TWO NEW SPECIES OF SEAGRASSES FROM AUSTRALIA, POSIDONIA SINUOSA AND P. ANGUSTIFOLIA (POSIDONIACEAE)

MARION L. CAMBRIDGE and JOHN KUO*

Department of Botany, University of Western Australia, Nedlands, W.A. 6009 (Australia) (Accepted 15 February 1979)

ABSTRACT Cambridge, M.L. and Kuo, J., 1979. Two new species of seagrasses from Australia, Posidonia sinuosa and P. angustifolia (Posidoniaceae). Aquat. Bot., 6: 307--328. Two new species of seagrass, Posidonia sinuosa and Posidonia angustifolia, from southern Australia, are described. These species are sympatric with the broad leaved Posidonia australis Hook. f., under which name they were previously known as "narrow leaved" forms. Morphological, anatomical and ecological data are presented as evidence for the separation of the species. The principal differentiating characters are the shape of the epidermal cells, the position of fibre cells in the leaf and leaf sheath, and the presence around the rhizome of strawlike fibres, derived from the disintegrating leaf sheaths. The species also differ in their habitat requirements, growth patterns and depth distribution.

INTRODUCTION

Seagrass communities form important elements of the near-shore marine vegetation on the south-western coast of Western Australia. The genus Posidonia is represented in them by at least four species. Three form major stands in embayments with relatively low wave energy around the southern coast of Australia and have been known under the one specific name of P. australis Hook. f. Another, recently named b y den Hartog (1970) as P. ostenfeldii, inhabits sand platforms subject to high wave energy. Womersley (1956, p. 84) first mentioned the possibility that "narrow leaved" and " b r o a d leaved" forms of P. australis might be t w o species and Wood (1959) described differences in leaf width and floral morphology in collections made from two tidal inlets on the eastern coast of Australia. Eichler (1965) also considered it probable that t w o distinct species, with marked differences in leaf widths, occur in South Australia. Den Hartog (1970) discounted these suggestions, drawing attention to a clump of P. australis which he found cast ashore during a storm, which had both narrow and broad leaves apparently growing from c o m m o n rhizomes. He attributed the differences in *Present address: Electron Microscopy Centre, University of Western Australia.

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leaf width to a mixture of vigorous and senescing plants of the same species growing within the same meadow. Shepherd (1974) and Shepherd and Womersley (1976) distinguished between "broad leaf" and "narrow leaf" forms for ecological studies of submerged communities in Spencer Gulf and St. Francis Island, South Australia, respectively. Cambridge (1975) found differences in morphology, habit and habitat preferences of these t w o forms in Cockburn Sound, Western Australia, and suggested they should be regarded as two species. Further confusion has arisen from drift collections of P. o s t e n f e l d i i being mistaken for one or other of the unnamed narrow leaved species of P o s i d o n i a in herbarium collections in Western and South Australia. Recent work on the ecology and t a x o n o m y of seagrasses in Western Australia has confirmed the suggestion that "narrow leaved" and "broad leaved" forms of P. australis should be recognised as two species, and has disclosed the presence of a third "narrow leaved" species previously included in the same taxon or in P. o s t e n f e l d i i . They can all occur sympatrically, b u t display clear differences in morphology, anatomy and habitat preferences. P o s i d o n i a o s t e n f e l d i i will be the subject of a similar taxonomic investigation, as several leaf forms are at present included in this taxon. PREPARATION OF MATERIAL F O R ANATOMICAL STUDY

Epidermal cells were stripped from leaves, m o u n t e d in water and photographed under bright field illumination. Free hand sections to show fibre distribution were stained in 0.05% toluidine blue, pH 4.4, for 30 s and m o u n t e d in water. Glycol methacrylate (GMA) sections and material for scanning electron microscopy (SEM) were prepared as in Kuo (1978). K E y FOR IDENTIFICATION OF L E A F FRAGMENTS OF P O S I D O N I A SPECIES ALLIED TO P. A U S T R A L I S

la.

Epidermal cells squamous, mostly as long as wide; leaves (6--) 10--15 (--20) mm wide when fresh, (5--) 8--13 (--18) mm when dry.

lb.

Epidermal cells elongate, 4--10 times as long as wide. 2a. Leaves narrow, 4--7 mm wide when fresh, with 7--11 nerves; epidermal cells elongate with smooth margins; fruits pyriform

. . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

P. australis.

P. a n g u s t i f o l i a

2b. Leaves broad (6--) 10--15 (--20) mm wide when fresh, with 14--21 nerves; epidermal cells squamous, as long as broad, with smooth margins; fruits falcate . . . . . . . . . . . . . . P. australis. KEY TO SPECIES ALLIED TO P O S I D O N I A A U S T R A L I S

la. Leaf sheaths brown and remaining membranaceous when old, splitting into strips when dry;leaves narrow, (4--) 7--9 (--11) mm wide when fresh, 1--2 per shoot, with 9--13 nerves; epidermal cells elongate with sinuous walls; fruits lanceolate in outline . . . . . . . . . . . . P. S i n u o s a

309 lb. Leaf sheaths disintegrating into pale fibres with age; 2--3 leaves per shoot. 2a. Leaves narrow, 4--7 m m wide when fresh, with 7--11 nerves; epidermal cells elongate with smooth margins; fruits pyriform . P. angustifolia. 2b. Leaves broad (6--) 10--15 m m (--20) wide when fresh, with 14--21 nerves; epidermal cells squamous, as long as broad, with smooth margins; fruits falcate . . . . . . . . . . . . . . . . . . . P. australis. NEW SPECIES Posidonia sinuosa Cambridge et Kuo, sp. nov. (Figs. 2, 5, 8, 11, 13, 14, 16, 18, 20a).

HOLOTYPE: Western Australia, Point Atwick, Garden Is., 20 Nov. 1971, M.L. Cambridge, Depth 3 m, in small bay sheltered by limestone reef. (holo: PERTH) Posidonia australi Hook. f. affinis, a q u a d i f f e r t : foliis (4--) 7--9 (--11) m m latis (inP. australi (6--) 10--15 (--20) mm); cellulis epidermalibus a vertice visis elongatis non squamosis, marginibus sinuatis, parietibus ad paginam folii verrucosis non laevibus; fasciculis fibrarum in foliis sub cellulis et epidermalibus et hypodermicis; vaginis foliorum aetate fuscantibus et membranaceis remanentibus, in fibris multis pallidis non findentibus; fasciculis fibrorum in vaginibus ad margines limitatis sine fibris lignosis per parenchymatem dispersis (in P. australi praesentibus); pedunculis sub anthesi ad 10 cm longis (in P. australi ad 30 cm), bracteis subter spicis linearibus non ad apices expansis; stigmate in flore immaturo cum processi irregulariter dentatis (in P. australi 3--5 hippocrepiformibus); connectivo antherae in flore immaturo in processos 3 extenso (non obtuso sparsim dentato ut in P. australi); fructibus lanceolatis nec complanatis nec falcatis. Roots. One, or rarely two, adventitious roots from the apical end of all or some rhizome nodes, 7--20 (--40) cm long, 0.1--2 m m diameter, white when new, reddish-brown and much branched when old. Rhizomes. Coarse, 5--8 m m diameter, monopodial, diffusely branched, laterally compressed, cream or pink in newest segments, near apex becoming brown in older segments; internodes varying in length from 1--50 mm; an amplexicaulous, sheath-like leaf base or scale leaf arising from each node; the leaf bases distichous. Rhizome branches terminal (formed only at the growing apex), in leaf axils a leaf-opposed colourless scale ensheathing each branch is present. Scales. 6--10 cm long, 5--10 m m wide, biauriculate, flaps overlapping for two thirds of the length, apices involute, obtuse to shallowly semilunar, not always symmetrical; retaining membraneous character but apices subject to disintegration, in early stages distinguishable from leaf sheath by absence of tannin deposition at the apex, indistinguishable when old.

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Leaf sheaths. 6--12 cm long, (4--) 5--10 (--11) mm wide, biauriculate, narrowed near the base, flaps overlapping to half way up the sheath, cream to pink brown, paler in fast-growing plants, darkening to brown when old and remaining intact; not disintegrating to straw-like fibres (Fig. 5), in contrast to P. australis (Fig. 4); ligula 1A--1/~mm long, straight or shallowly semilunar, margins dark reddish brown .with tannins after shedding of leaf; auriculae 1--2 mm tall, IA--1 mm wide; in cross section abaxial fibre bundles immediately below the epidermal cells, present in all portions of sheath including the flaps; adaxial fibre bundles below the hypodermis and absent from the flaps, non-adaxial fibre bundles also scattered sparsely among the parenchyma tissues. Leaf blades. 1--2 per shoot; (2--) 30--70 (--120) cm long, (4--) 7--9 (--11) mm wide, 160--230 pm thick 5 cm from base, of equal width along entire length, slightly convex in cross section; apex obtuse, emarginate or truncate, often asymmetrical, margin entire, longitudinal vascular bundles parallel, (8--) 9--13, one of the central bundles more conspicuous than others, interconnected b y transverse vascular bundles at intervals of 1--4 mm. Epidermal cells elongate, 4--12 times as long as wide, cell margins in surface view sinuous, (Fig.8), outer wall thickened with knob-like projections, verrucose in surface view ( F i g . l l ) , in contrast to P. australis (Fig.10); in cross section, the epidermal surface forming a pallisade (Fig.13), in contrast to P. australis (Fig.12); fibre bundles below both epidermal and hypodermal cells. Inflorescence. Borne terminally on unspecialised shoot, held a b o u t 10 cm above substrate, cryptic beneath leaf canopy. Peduncle. Compressed laterally, 8--15 cm tall, generally emerging only 10 cm above substrate, spikes 4--6 cm long, subtended by one long and one short bract, consisting of a blade (5--) 10--25 cm and 1--7 cm long, respectively, and a compressed biauriculate and ligulate sheath, blades of constant width 5--8 mm, apex truncate to obtuse; three to five higher bracts subtending spikes; each bract consisting of a short blade, 3--20 mm long, sometimes absent; and a sheath 4--6 mm long, flaps 21A mm wide, not overlapping or only near their base; ligula and auriculae reduced or absent. Spikes. 2--4, 1--5 cm tall, less than 1 cm before anthesis, then elongating, each spike consisting of 3--4 (--6) sessile, alternate, hermaphrodite flowers, uppermost flower maturing first, terminal spur 3"-6 mm tall. Stamens. Three per flower, consisting of 2 parallel thecae 31/~--5 mm tall; thecae sessile on connective, red before shedding pollen, with mucronate apex, dehiscing longitudinally and outwardly to release white filiform pollen, blackening, then deciduous one week after pollen shedding, leaving a linear callus; connective 4--6 m tall, oblong--lanceolate, strongly keeled, apex tridentate (Fig. 20a) but losing processes after emergence from bracts

311 and becoming obovate; connectives persistent as 3 claws at the base of the developing seed; pollen 1 mm long. Gynoecium. 4--5 mm tall, ovary single, carpel oblong--ellipsoid, bearing stigma; stigma irregularly dentate, generally with 3--5 spurs, astylous. Fruit. Lanceolate in outline, 21/~--31~ times as long as wide, smooth, mature length up to 20 mm, bearing brown remains of stigma at apex, terete in cross section, pericarp fleshy, green, then yellow and brown after shedding of seeds, brown when dry, opening by splitting from the base along 2--3 indeterminate sutures. Flowers mature in spring, seeds shed in early summer. Seed. Ellipsoid, 15--20 mm long, oblate in cross section, dorsal side thicker than ventral side, twice as high as wide; dorsally convex with longitudinal ridge, seed coat forming a brown membranous ventral wing 2--3 mm wide with many tannin cells; ventral and dorsal apices of wing extending into 2 points protecting the epicotyl; the bulk of seed consisting of fleshy storage tissue, with tannin cells; central trace connecting apical embryonic leaves and root with distal portion of embryo; shoot axis 1/3---1/2 as long as storage organ; epicotyl 6 mm, straight becoming curved, green, consisting of ensheating green coleoptile and plumula linear leaves 2--3 mm wide merging even before shedding of the pericarp. First root as a bud central to the shoot axis, development delayed until burial of the seed or not developing. Seedling. Storage organ retained for one to t w o years after germination; coleoptile retained as dark brown remnants subtending the shoot axis; leaf sheaths brown and membranous after shedding of leaf as in mature plant; leaves linear b u t stunted, 2 per shoot; rhizome white to pink, nodes formed b y ensheathing leaf sheaths, branching within months of germination, branches ensheathed by colourless scale leaf; roots white, oldest roots finely branched. Distribution and habitat Posidonia sinuosa is widely distributed in marine embayments and nearshore areas on the western and southern coasts of Australia. In Western Australia it reaches its northern limit at Shark Bay (25°S, l13°E) and on the southern coast its eastern limit is Kingston, South Australia (35°S, 140°E) (Kingston, 21 March, 1974, S.A. Shepherd, 6 m deep, ADU A46462). Its distribution thus corresponds to that of P. australis on the western and southern coast, but P. australis has a wider distribution on the eastern shores of Australia, being represented by extensive meadows at Corner Inlet, Wilsons P r o m o n t o r y in Victoria (39°S, 146°E), and the New South Wales coast in embayments such as Jervis Bay and Botany Bay, and estuaries north to Macquarie (31°S, 135°E).

312 In embayment situations P. sinuosa and P. australis occur sympatrically, but in less enclosed waters such as Geographe Bay, 200 km south of Perth, Western Australia (33.5°S, 115°E), P. sinuosa alone forms meadows with Amphibolis spp. Material examined (selection only). Western Australia. Quindalup Beach, Geographe Bay; 14 Aug., 1976, M.L. Cambridge (plants with buds) (K). Safety Bay, Warnbro Sound; 26 Oct., 1978, M.L. Cambridge (incl. young fruits) (CANB). Dunsborough, Geographe Bay; 18 Sept., 1976, M.L. Cambridge (incl. mature seeds near shedding) (AD). Shoalwater Bay; 24 Feb., 1974, M.L. Cambridge (2 and 14 month old seedlings) (PERTH). Shoalwater Bay; 24 Feb., 1974, M.L. Cambridge (leaf bases pale and extended in response to inundation by sand at the edge of a small sand patch) (PERTH). N. of Busselton Jetty, Geographe Bay; May 1976, M.L. Cambridge (dark, abraded leaf sheaths collected from eroding meadow raised above surrounding sand, a few stiff fibres present in the sheath but no development of fibre masses like P. australis) (PERTH). Turtle bay, E. Wallaby Is, Houtmans Abrolhos; 7 April, 1978, M.L. Cambridge (6 m deep, adjacent to coral reef on calcareous sand) (SYD). Arid Bay, C. Arid; 6 May, 1977. M.L. Cambridge (on siliceous sand with Amphibolis griffithii (Black) den Hartog, 4--10 m then replaced by P. ostenfeldii) (MEL). South Australia. Port Elliot; 1894, J.L. Hussey, 528969 (MEL). Encounter Bay; Jan. 1926, J.B. Cleland, 96730021 (AD). Port Augusta, Spencer Gulf; 28 Oct., 1973, M.L. Cambridge (in patches at 4 m adjacent to Playford Power Stn.) (PERTH). Marino Beach; 28 Aug., 1977, M.L. Cambridge (with Amphibolis sp. and P. angustifolia on quartz sand, 3--4 m.) (PERTH). Posidonia angustifolia Cambridge et Kuo, sp. nov. (Figs.3, 6, 9, 15, 17, 19, 205).

HOLOTYPE: Western Australia, 4 km NE of Cape Naturaliste, 22 Nov., 1976, M.L. Cambridge, 30 m deep, on fine quartz sand with old shells and limestone nodules; forming patches 5--6 m diam. with sparse Heterozostera tasmanica (Martens ex Aschers.) den Hartog and Halopila ovalis (R. Br.) Hook. f., occasional flowers, (holo. : PERTH (Fig. 3), iso. : AD, K). Posidonia australi Hook. f. affinis, a qua differt: foliis 4--6 mm latis (in P. australi (6--) 10--20 mm); cellulis epidermalibus a vertice visis elongatis non squamosis, marginibus laevibus, parietibus ad paginam folii laevibus; fasciculis fibrarum in foliis on nisi sub cellulis epidermalibus; vaginis foliorum in fibris paucis tenuibus pallidis findentibus aetate non fuscantibus; fasciculis fibrorum in vagini consistentibus e fibris lignosis paucis per parenchymatem dispersis ut in P. australi sed fasciculis fibrorum adaxialibus sub hypodermate (in P. australi

313 sub epidermide); pedunculis sub anthesi ad 15 cm longis (in P. australi ad 30 cm); stigmate in flore immaturo cum processi 2--3 leavibus (in P. australi 3--5 hippocrepiformibus); connectivo antherae in flore immaturo in processum 1 extenso (non obtuso sparsim dentato ut in P. australi) fructibus pyriformibus parum complanatis, non falcatis. Habit like P. sinuosa, differing in form in the following characters:

Roots and rhizomes. As for P. sinuosa, rhizomes 4--6 mm in diam., internodes varying in length, 1--60 mm. Scale leaf as for P. sinuosa, apex obtuse. Leaf sheaths. 5--12 cm tall, 4--6 mm wide, flaps overlapping to two-thirds way up the sheath, cream, disintegrating within 6 months to fine strawlike fibres (Fig. 6) b u t sparser than P. australis (Fig. 4), ligule to 1 mm long, shallowly semi-lunar, auriculae 2 mm tall. A n a t o m y of sheath as for P. sinuosa with the exception of the adaxial fibre bundles which lie beneath the epidermis. Leaf blades. As for P. sinuosa, differing in the following: 2--3 per shoot, (10--) 20--75 cm long, 4--6 mm wide, about 160 tim thick 5 cm from base, with 7--11 longitudinal vascular bundles, not concave--convex in transverse section. Epidermal cells elongate 3--6 times as long as wide, cell margins smooth, not sinuous in surface view, epidermal surface smooth, not verrucose, fibre bundles lying beneath the epidermis, not beneath the hypodermis. Inflorescence. As for P. sinuosa, usually held 10--15 cm above substrate. Peduncle. 10--18 cm long, 2 mm wide. Stamens. As for P. sinuosa, differing in the following: anther connective in immature flowers with acuminate apex and entire margin best observed in flowers before their emergence from the protection of the bracts (Fig. 20b). Gynoecium. Stigma with 2 (--3) spurs, not dentate. Fruit. As for P. sinuosa, differing in the following: 2.5 cm long, 1--1.2 cm wide, asymmetrically pyriform, 2--3 times as long as wide, only slightly compressed in transverse section. Seedlings n o t collected. Distribution and habitat Posidonia angustifolia has so far been found to extend from Houtmans Abrolhos on the Western Australian coast (29°S, 114°E) to St. Vincent Gulf in South Australia (34°S, 138°E) on substrate combining fine sand with cobble-sized fractions. Depths range from 2--35 m in open near-shore waters rather than sheltered embayments. At shallower depth and in relatively

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sheltered situations (e.g. adjacent to a coral reef, Houtmans Abrolhos, W.A. and Marino, S.A.) P. angustifolia occurs sympatrically with P. sinuosa and Amphibolis spp. At depths of 35 m it has been observed with sparse Heterozostera tasmanica and Halophila ovalis. Material examined (selection only). Western Australia. Houtmans Abrolhos, Turtle Bay, E. Wallaby Is.; 7 Apr., 1978, M.L. Cambridge (PERTH). Bunbury; Feb., 1975, L. Collins, (23.7 m deep, fine quartz sand) (PERTH). Bunbury; 3 Dec., 1977, M.L. Cambridge, 20 m deep (L.) Warnbro Sound; 3 Dec., 1977, M.L. Cambridge, (abundant fruits in drift with P. ostenfeldii fruits) (PERTH spirit coll.). Ringbolt Bay, E. of C. Leeuwin; 16 Nov., 1976, M.L. Cambridge, (in shelter of granite rocks on 0.5 m veneer over reef, 3--4 m, patches 10--20 m in diam. surrounded by Amphibolis griffithii, (MEL). Mouth of Pallinup R., west of C. Riche; 26 May, 1977, M.L. Cambridge, (fragment in drift), (PERTH). South Australia. Encounter Bay; 11 May, 1924, B.J. Cleland AD96730023, (AD). Grange; 30 Apr., 1938, C.M. Eardley 96405013, (AD). North Bay, Pearson Is. Eyre Peninsula; 11 Jan., 1969, J.E. Watson 124413, (50' deep D.E.S. 6669), (SYD). Marino Beach; 29 Aug., 1977, M.L. Cambridge, (4--5 m on fine sand with cobbles from adjacent cliff with Amphibolis griffithii and P. sinuosa), (PERTH). DISCUSSION

Taxonomy Den Hartog (1970) listed four synonyms for P. australis Hook. f. (1868): Caulinia oceanica auct. non DC:R.Br., Prodr. Nov. Holl.1 (1810) 339. Amphibolis zosterifolia F.Muell., Fragm. 4 (1864), 113--114, flower only. Caulinia australiana F. Muell., Fragm. 6 (1868), 198. Alga australis 0. Kuntze, Rev. Gen. P1.2 (1891), 744. In order to define the status of the seagrasses allied to P. australis, after establishing that there is one "broad leaved" species and two "narrow leaved" species, Hooker's type material was examined and the synonymy listed above traced to the original descriptions. Hooker (1860) recognised Caulinia oceanica

Fig. 1. Posidonia australis Hooker f. Lectotype sheet (Gunn, 1347, K). Fig. 2. Posidonia sinuosa nov. sp. holotype, Pt. Atwick, Garden Is., W.A. (Cambridge, 20.XI.1971, to be lodged at PERTH). Fig. 3. Posidonia angustifolia nov. sp. holotype, C. Naturaliste, W.A. (Cambridge, 22.XI.1976; to be lodged at PERTH).

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sensu R. Br. as s y n o n y m o u s with P. australis and listed t w o specimens in the protologue. The first was from the R. Brown collection at BM, Bennett No. 5817, originally determined as Caulinia oceanica, collected from southern Australia and described b y Brown (1810), w h o linked the species with the European C. oceanica, later Posidonia oceanica (L.) Delile. Hooker (1860, p. 43) noted this specimen as being collected form " t h e southern coast of Tasmania" b u t Brown, in his original description, simply listed the location as "M.D."; " M " encompassing the southern coast from Cape Leeuwin at the west to the islands of Bass Strait and Wilsons P r o m o n t o r y in the east and " D " signifying Tasmania, particularly the northern and southern coasts, where Brown collected around Georgetown and Hobart. The leaves of this material are 7---8 mm wide. The leaf epidermal cells examined from the right hand specimen on this sheet are as long as broad and n o t elongate. Another sheet of Brown's at BM, consisting only of four Posidonia inflorescences (Bennet No. 5812), does not appear to have been viewed b y Hooker, for in the protologue he stated that he had not seen flowering material. This material is discounted from t y p e status. The material is probably P. australis because of the long peduncles. The second collection listed in Hooker's protologue is Gunn 1347 at K with a description of the collection site "in sea, below water level, growing in beds, Georgetown". With its greater development of a mass of fibres from the leaf sheaths, and leaves 8 mm wide, this specimen corresponds better than Brown 5817 to Hooker's description of P. australis, viz. with rhizomes "densely covered with long ragged white fibres, 2--3 inches long, the remains of old leaves". Hooker also described the leaves as " 1 / 3 broad" (8 mm) and the leaves "shining", both characters fitting this specimen. Microscopic examination of the leaf epidermal cells showed them to be as long as broad (B. Maslin, personal communication, 1976). For these reasons, the Gunn 1347 specimen at K, and shown in Fig. 1, is here selected as the lectotype of P. australis and the Brown collection 5817 at BM as the paratype, although examination of the leaf epidermis has shown that b o t h are the same species. Caulinia australiana F. Mueller was described from a collection at King George Sound, Western Australia. Mueller's (1868) description leaves no d o u b t that the specimen is the broad leaved P. australis and not one of the allied narrow leaved species, as he described the leaves as being broad and flat, with 16--20 nerves. It also described the flowers as having a stigmatic surface with 4 lobes and elongate anther connectives without a mucro, b u t this latter character is n o t particularly useful as it could apply to mature flowers of any of the three allied species. The first description of the flowers and fruit Fig. 4. P. australis old leaf sheaths forming masses of pale fibres like goats hair. Fig. 5. P. sinuosa old leaf sheaths remaining membraneous, splitting into strips when dry; scale as for Fig. 4. Fig. 6. P. angustifolia old leaf sheaths forming a few pale fibres around the rhizome; scale as for Fig. 4.

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of P. australis was by Mueller (1864) in which he mistook the inflorescence of P. australis for the female flower of A mphibolis zosterifolia (= A. antarctica (Labill.) Sonder et Aschers. ex Aschers.). Kuntze (1891) proposed Alga australis O.K. as a new name for P. australis Hook. f. but included no description of new material. Den Hartog (1970, p. 121) classes the genus Alga as nomen rejiciendum. The existence of two species differentiated on the basis of leaf width has long been suspected (Womersley, 1956; A.M. Baird, personal communication, 1976). Wood (1959) was the first to present evidence of morphological differences, with a form from Merrimbula having a long narrow leaf and 6 anthers per pistil as shown in his Fig. 1a--b, and one from Port Hacking with a shorter, broader leaf and 3 anthers per pistil as shown in his Fig. lc--d. Den Hartog (1970) discounted these differences after critically examining Wood's drawings, commenting that the Merrimbula form was a normal P. australis flower and that the Port Hacking form was drawn inaccurately as he had examined material from Port Hacking and found it to be normal P. australis. Our present knowledge of the distribution of the narrow leaved species allied to P. australis indicates that they go no further east than Victoria and P. angustifolia probably no further than South Australia, whereas P. australis is present in estuaries north of Sydney. Thus, den Hartog's interpretation of the Wood drawings as being both of P. australis appears to be correct. Eichler (1965) considered that two species existed in South Australia with marked differences in leaf width. Den Hartog (1970) discussed the possible existence of two species but on finding a clump of P. australis cast up in the storm drift at Safety Bay, Western Australia, in which both narrow and broad leaved shoots formed the terminal branches of the same rhizome system, he concluded that narrow leaved specimens were a product of "senility of the rhizome system". Den Hartog was probably correct in this interpretation, as it is likely that he was examining a clump of P. australis and not a mixture of

Fig. 7. P. australis leaf epidermis, surface view; cells squamous with smooth margins. Fig. 8. P. sinuosa leaf epidermis, surface view; cells elongate with sinuose margin; scale as for Fig. 7. Fig. 9. P. angustifolia leaf epidermis, surface view; cells elongate with smooth margins; scale as for Fig. 7. Fig. 10. P. australis leaf epidermis under SEM; smooth surface without projections. Dark lines are an artifact of vacuum dehydration, small bodies on surface are bacteria. Fig. 11. P. sinuosa leaf epidermis under SEM; verrucose surface produced by projection of the cell walls at the leaf surface; scale as for Fig. 10. Fig. 12. P. australis leaf epidermis longitudinal section, GMA sections stained with PAS and toluidine blue; cells squamous (E), fibre (F) beneath epidermis. Fig.13. P. sinuosa leaf epidermis longitudinal section, cells elongate (E), cell wall projections at leaf surface; stained as for Fig.12.

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321

Fig. 20. Another connective with thecae. Apex tridentate in P. sinuosa (left) and entire in P. angustifolia (right). Mag. x 20.

t a x a , b u t t h e c o n f u s i o n arose b y a t t e m p t i n g t o define t h e s e p a r a t e t a x a o n l y f r o m l e a f width. O n e o f us (M.C.) has o b s e r v e d t h e s t u n t i n g o f leaves f r o m b o t h p o l l u t i o n a n d n a t u r a l l y u n f a v o u r a b l e c i r c u m s t a n c e s a n d this applies f r e q u e n t l y t o d r i f t m a t e r i a l w h i c h is o f t e n growing in marginal h a b i t a t s subj e c t t o s t o r m erosion. L a r k u m {1976) c o n s i d e r e d t h a t o n l y o n e species, P. australis, was p r e s e n t in B o t a n y Bay a l t h o u g h t h e leaf w i d t h o f s o m e s a m p l e s was o n l y 7 - - 8 m m . He a t t r i b u t e d t h e d e v i a t i o n in t h e leaf w i d t h f r o m t h e n o r m o f 1 1 - - 1 2 m m t o s t u n t i n g o f plants a t t h e l o w e r e n d o f t h e d e p t h range. S h e p h e r d ( 1 9 7 4 ) i n d i c a t e d d i f f e r e n c e s in h a b i t a t p r e f e r e n c e s o f t h e b r o a d a n d n a r r o w leaved " m o r p h " w i t h t h e b r o a d leaf c o m m o n e s t b e t w e e n 2 a n d

Fig.14. P. sinuosa leaf transverse section stained with 0.05% toluidine blue and PAS counterstaining, showing position of fibre bundles (arrowed) in relation to epidermis and hypodermis. A = air-lacuna; V = vascular bundle. Fig. 15. P. angustifolia, as for Fig. 14. Fig. 16. P. sinuosa fibre bundles (F) beneath both epidermis (E) and hypodermis (H) similar to P. australis; stained as for Fig. 14. A = air-lacuna; V = vascular bundle. Fig. 17. P. angustifolia fibre bundles (F) beneath epidermis (E) only; stained as for Fig. 14. A = air-lacuna; V = vascular bundle. Fig. 18. P. sinuosa leaf sheath free-hand transverse section, stained with toluidine blue showing position of abaxial fibre bundles (F) in relation to epidermis (E) and hypodermis (H). Showing fibre bundles beneath hypodermis only. Fig. 19. P. angustifolia fibre bundles (F) beneath the epidermis (E) only; stained as for Fig. 18. A = air-lacuna.

322 6.5 m depth and the narrow leaf patchy between 4 and 8 m on the eastern shore of Spencer Gulf, but noted t h a t the vertical distribution was much less marked than on the opposite shore where the broad leaf was confined to the shallow tops of plateau-like sand banks and the narrow leaf to the sloping sides to a depth of 8 m.

Characters for separation o f species The best characters for separation of the Australian Posidonia species are the leaf sheaths and leaf widths (Table I), and at the micro level, the epidermal cells and fibre bundles in the leaf. Although fertile material is n o t always available through the range of the species, the forms of the seeds also display clear specific differences. Epidermal cells need no preparation for examination; dried material can be rehydrated in water, and fresh material needs only mounting in water and examining under a light microscope (Figs.7--9). The distribution of fibre bundles can be examined easily in fresh hand sections stained for 30 s with toluidine blue and m o u n t e d in water (Figs.14--19). Tables I and II show t h a t each of the three species has some characters in c o m m o n both at the macroscopic and microscopic level. Reliable field identification of sterile material can be made by including rhizome material with the remnants of leaf sheaths along with the collection of leaves (Table III). The older leaf sheaths of P. sinuosa generally remain membranous for several years so that the rhizomes tend to be clad in dark scales rather than pale fibres. The leaf sheaths of both P. australis and P. angustifolia become fibrous, but the range of leaf widths does not overlap (4--7 mm for P. angustifolia and generally greater than 10 mm for P. australis). The rhizomes of P. australis are also more fibrous and robust than those of P. angustifolia. Although populations of each of the three species can generally be identified using leaf widths, since P. australis and P. angustifolia rarely overlap the width range of P. sinuosa, individual plants should not be identified using only leaf width. Even in a vigorously growing population of P. australis where the widths of most leaves lie within the range of 12--18 mm, there will be a few leaves as low as 6 m m produced as the first leaf on a new branch, particularly if vigorous branching of the rhizome has already occurred. As leaves o f P. sinuosa and P. angustifolia have a smaller width range within any one population, these species are less of a problem. Leaf width as a character is most unreliable in populations deteriorating through natural or man-made causes. Older portions of the leaves of P. sinuosa develop a markedly concavo-convex cross section. Leaves of P. australis and P. angustifolia are planar and develop a pronounced shoulder from thickening of the margins. Leaves in all three species are thickest in cross section near the base and thinnest towards the apex with elongation and collapse of the septate air-lacunae. Dimensions vary with vigour, but in general the cross-section of P. australis is twice that of P. sinuosa and P. angustifolia.

323

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324 TABLE II Comparison of anatomical and morphological characters in Posidonia australis, P. sinuosa and P. angustifolia P. australis

P. sinuosa

P. angustifo]ia

(6--) 10--15 (--20) broad

(4--) 7--9 (--11) narrow

4--6 narrow

Longitudinal vascular bundles

14--20

9--13

7--11

In cross-section (mature portion)

Planar

Convex--concave

Planar

Epidermal cells in surface view

Margins smooth, cells compressed, 1/2---1 × long as wide

Margins sinuous, cells elongate, 4--12× long as wide

Margins smooth, cells elongate, 3---6× long as wide

Epidermal surface

Smooth

Verrucose

Smooth

Most fibre bundles lie beneath

Epidermis and hypodermis

Epidermis and hypodermis

Epidermis only

1/3

1/2

2/3

Hypodermis

Epidermis

Disintegrates into masses of straw-like fibres

Darkens, remains membraneous, not developing masses of fibres

Disintegrates into a few straw-like fibres

15--45

5--10

5--15

Expanded toward apex

Linear

Linear

1. Leaf blade Leaf width (mm)

2. Leaf sheath Flaps overlapping

Most adaxial fibre Hypodermis bundles lie beneath Leaf sheath aging 6--12 months

3. Inflorescence Length of mature peduncle (cm) Bracts

4. Immature flowers Apex of anther

Obtuse

Mucronate

Obtuse

Apex of anther connective

Obtuse, 3--5 small irregular teeth

Tridentate

Acuminate

Stigma

3 irregular processes forming a horseshoe

3--5 long processes secondarily dentate, forming crown

2--3 smooth processes

Falcate

Lanceolate

Pyriform, asymmetrical

Laterally compressed

Terete

Slightly compressed

5. Fruits Outline T.S.

325

Species are most reliably identified from leaf material at the microscopic level, using characteristics of the epidermal shape and cell margins (Figs. 7--9) and the distribution of fibre bundles in the leaf and leaf sheath (Figs. 14--19). The block-like leaf epidermal cells of P. australis (l/r-1 times as long as wide) are distinct from the elongate cells of P. sinuosa (4--12 times as long as wide) and P. angustifolia (3--6 times as long as wide). The epidermal cells of P. sinuosa differ markedly from those of P. angustifolia and P. australis in having the sinuous margin of the cells visible as wavy lines between the cell contents (Figs. 7--9). The species epithet for P. sinuosa is based on this character. These epidermal characters remain constant in the epidermis of b o t h petiole and the long bracts subtending the spikes so that collections consisting only of inflorescences can still be reliably identified. The position of fibre bundles in the leaf and leaf sheath was first used by Sauvageau (1890) to distinguish P. angustifolia (misdetermined by Sauvageau as P. australis) from the mediterranean P. oceanica (L.) Delile, and b y Ostenfeld (1916) to distinguish P. australis from an undescribed species of Posidonia collected in southern Australia, later to be described by den Hartog (1970) as P. ostenfeldii. Leaf fibre bundles of P. australis and P. sinuosa lie beneath both epidermis and hypodermis, b u t in P. sinuosa more bundles are associated with the hypodermis (Fig. 14). In P. angustifolia the fibre bundles lie beneath the epidermis only (Fig. 15). The position of the adaxial fibre bundles in the leaf sheath can also be used to distinguish species. Bundles lie beneath the epidermis of P. angustifolia (Fig. 19), whereas they lie beneath the hypodermis of P. sinuosa (Fig. 18) and P. australis. Floral characters and the form of the scale leaf or prophyll enclosing new branches differ consistently between the species b u t are less useful than those of leaf and leaf sheath. For example, floral characters apply to immature spikes dissected from the bracts before anthesis, as details are often eroded once the flowers emerge from the protection of the bracts. This applies particularly to the apex of the anther connective and the processes on the stigma surface. Suitable material occurs only briefly during the spring flowering period. Similarly, the scale leaf associated with rhizome branching is rare in P. sinuosa and P. angustifolia as these species branch less frequently than P. australis. Characters developed in response to environment create superficial differences between species, b u t collections from different habitats have demonstrated the plasticity of these characters. For example, the leaves of all specimens so far collected of P. angustifolia are flexuose, b u t so are those of P. australis and P. sinuosa specimens collected from areas subject to consistent wave action. Another example is the colour of the leaf sheath of P. sinuosa, which tends to be dark brown in colour. However, rapidly growing P. sinuosa has pale leaf sheaths which can be very similar in colour to those of P. australis, as the tannin deposition colouring the sheaths appears to be affected b y the growth rate.

326

Distribution and habitat The three species share a c o m m o n range on the southern coast of Australia, but P. sinuosa and P. angustifolia do not appear to extend further east than Kingston, South Australia. In contrast, P. australis continues east to Corner Inlet, Victoria, and then occurs in embayments and estuaries on the east coast to Macquarie, New South Wales. On the west coast, the most northerly major stands o f P . australis and P. sinuosa occur around Shark Bay (26°S). Ostenfeld (1916) collected P. australis at Carnarvon and there are reports of Posidonia meadows on the remote coastline north of Point Quobba (24.5°S) (B.W. Logan, personal communication, 1977). P. angustifolia on the west coast has been collected only as far north as Houtmans Abrolhos (28°S) but as collecting in the area has been sporadic, subsequent surveys may extend the range. Habitat differentiation can be distinguished despite the occurrence of sympatric populations. P. australis and P. sinuosa are generally restricted to less than 15 m, whereas P. angustifolia grows to at least 35 m depth. The sympatric occurrence of species with different habitats is attributed to

T A B L E III C o m p a r i s o n o f ecological a n d m o r p h o l o g i c a l c h a r a c t e r i s t i c s f o r field i d e n t i f i c a t i o n

P. australis

P. sinuosa

P. angustifolia

1. D e p t h range*

L.W.--15 m

L.W.--15 m

2--35 m

2. H a b i t in well developed meadows

Continuous cover

L i n e a r rows, u p t o 50 c m wide, parallel t o prevailing d i r e c t i o n of water movement

Continuous cover

3. N u m b e r o f leaves per shoot

2--3

1--2

2--3

4. Leaf w i d t h ( m m )

(6--) 10--15 (--20)

(4--) 7--9, (--11)

4--6, n a r r o w

broad

narrow

5. L e a f cross-section (mature portion)

Planar

Convex--concave

Planar

6. Leaf base ageing 6--12 months

Disintegrates i n t o masses o f straw-like fibres

Darkens, r e m a i n s membraneous, no fibres

Disintegrates i n t o a few pale fibres

7. P o s i t i o n of m a t u r e flowers a n d fruits

Held a b o v e leaf c a n o p y

Hidden beneath leaf c a n o p y

Hidden beneath leaf c a n o p y

*L.W. = l o w water.

327

localised differences in sedimentation, to be discussed in a subsequent paper. P. australis appears tO occur in areas of active sedimentation, whereas P. sinuosa flourishes in areas where sedimentation is much less. Its pattern of growth in rows with bare sand b e t w e e n the rows appears to be a response to restricted sediment supply. From this investigation on species allied to Posidonia australis, the identity of species included in ecological studies can be determined. In Cockburn Sound, ecological studies mentioned in Cambridge (1975) were carried o u t on P. australis and P. sinuosa b u t the survey in South Australia by Shepherd and Sprigg (1976) included P. australis, P. sinuosa and P. angustifolia. ACKNOWLEDGEMENTS

We thank Mr. B. Maslin (PERTH) for his examination and comments on t y p e material held in London, Mr. Alex George (PERTH) for the Latin translation and taxonomic advice, Assoc. Prof. A.J. McComb (University of Western Australia) for editing, Miss A. Huber (University of Western Australia) for botanical drawings, Prof. H.B.S. Womersley and Mrs. E. Robertson (University of Adelaide) for helpful discussion, Dr. S. Jacobs (SYD), Miss H.I. Aston (MEL), Dr. H.J. Eichler (CANB), Dr. J. Jessop (AD) and Dr. S.C. Ducker (Melbourne University) for allowing us to examine their collections. Special thanks are due to Mrs. M.M. Sedlak for typing drafts of this manuscript. Our thanks are also extended to those who helped field collections to be made over the full geographical range of the species, particularly Dr. E.D. Hodgkin, Western Australian Department of Conservation and Environment, Mr. R. Lenanton of the Western Australian Department of Fisheries and Wildlife and Dr. B. Wilson, Western Australian Museum for their invitations to accompany expeditions to remote coasts. Mr. L. Collins collected deepwater specimens during offshore drilling programs of the Geology Department, University of Western Australia, and Mr. S. Shepherd and Mrs. J. Watson kindly facilitated collecting in South Australia, Victoria and New South Wales.

REFERENCES Brown, R., 1810. Prodromus florae Novae Hollandiae et insulare Van Diemen. p. 339. Cambridge, M.L., 1975. Seagrasses of South-Western Australia with special reference to the ecology of Posidonia australis Hook. f. in a polluted environment. Aquat. Bot., 1: 149--161. Den Hartog, C., 1970. The Seagrasses of the World. Verh. K. Ned. Akad. Wet. Afd. Natuurkd., l~eeks 2, 59: 1--275. Eichler, Hi., 1965. Supplement to J.M. Black's Flora of South Australia (second edn., 1943--1957). Govt. Printer, Adelaide, p. 37. Hooker, J.D., 1860. Flora Tasmaniae. Vol. II. Lovell Reeve, London, p. 43. Kuntze, C.E.O., 1891. Revisio Generum Plantarum, Vol. 2. p. 744.

328

Kuo, J., 1978. Morphology, anatomy and histochemistry of Australian seagrasscs of the genus Posidonia K~nig (Posidoniaceae). I. Leaf blade and leaf sheath of Posidonia australis Hook. f. Aquat. Bot., 5: 171--190. Larkum, A.W.D., 1976. Ecology of Botany Bay. I. Growth of Posidonia australis (Brown) Hook. f. in Botany Bay and other bays of the Sydney Basin. Aust. J. Mar. Freshwater Res., 27: 117--127. Mueller, F. yon, 1864. Fragmenta phytographiae Australiae. Vol. 4. Govt. Printer, Melbourne, p. 114. Mueller, F. yon, 1868. Fragmenta phytographiae Australiae. Vol. 6. Govt. Printer, Melbourne, pp. 198--199. Ostenfeld, C.H., 1916. Contributions to Western Australian Botany, Part 1. Dan. Bot. Ark., 2: 1--44. Sauvageau, C., 1890. Observations sur la structure des feuilles des plantes aquatiques. J. Bot., 4: 237--245. Shepherd, S.A., 1974. An underwater survey near Crag Pt. in upper Spencer Gulf. S. Aust. Dept. Fish. Tech. Report 1, pp. 1--29. Shepherd, S.A. and Sprigg, R.C., 1976. Substrates, sediments and subtidal ecology of Gulf St. Vincent and Investigator Straight. In: C.R. Twidale, M.J. Tyler and B.P. Webb (Editors), Natural History of the Adelaide Region. Roy. Soc. S.A. Publ. No. 5, pp. 160--174. Shepherd, S.A. and Womerley, H.B.S., 1976. The subtidal and seagrass ecology of St. Francis Island, South Australia. Trans. R. Soc. South Aust. 100: 177--191. Wood, E.J.F., 1959. Some east Australian seagrass communities. Proc. Linn. Soc. N.S.W., 84: 218--226. Womersley, H.B.S., 1956. The marine algae of Kangaroo Island. IV. The algal ecology of American River inlet. Aust. J. Mar. Freshwater Res., 7: 64--87.