Thalassia hemprichii Asch.

Roots with longitudinal air-channels, septations c. 1.75 mm spaced; some roots erect, with thickened top. Leaves 10-40 cm by 4-11 mm. Male plants with 1-2 inflorescences; peduncles in the male plants c. 3 cm, those in the female plants 1-1.5 cm, after anthesis elongating to 2-4 cm. Spathal segments lanceolate, acute (apices unequal in size), entire, persistent (according to Hook. f. Trim. Fl. Ceyl. 4 1898 127 caducous), 2-2½ by 0.5 cm, with many short, brown dashes. Pedicels of the male flowers 2-3 cm; ♀ flowers subsessile, after anthesis very shortly pedicelled. Perianth segments revolute, light brown, 7-8 by 3 mm. Stamens 3-12; anthers oblong, occasionally forked, 7-11 by 1-1.25 mm; pollen grains 20-33 μ. Ovary conical, 1 cm, its rostrum 2-3 cm; styles 6, at 1/3 from the base split into 2 filiform arms, each on the underside with 2 longitudinal grooves, light brown, after anthesis curling and caducous, 1.5-2 cm. Fruit globose, rugose, light-green, bursting open with c. 20 valves, 2-2.5 by 1¾-3.25 cm. Seeds 3-9, 8 by 8 mm, the thickened basal portion dark-brown; cotyledon greenish.

Common on muddy coral-sand in sheltered, shallow bays, also in pools on tidal flats in open bays, where ocean currents and wave action are not so strong. It forms together with other sea-grasses extensive submarine meadows, wherein it sometimes predominates, e.g. at Honduras Bay (Mindoro); there it lives, according to Pascasio & Santos Bull. Nat. & Appl. Sc. Philip. 1 1930 1-19 5 pi. , together with 6 other sea-grasses, viz Halophila ovalis, H. spinulosa, Enhalus acoroides, Cymodocea serrulata, C. rotundata, and Diplan-thera uninervis. It occurs from low watermark, where at ebb-tide it sometimes falls dry, to 5 m depth, depending on the lucidity of the water, but below 3.5 m depth it does not form a closed vegetation, and is replaced as dominant species by sterile Enhalus acoroides. After storms and in certain monsoons the leaves are often washed ashore in large quantities.The fruit of Thalassia hemprichii ripens below the water surface, and has no buoyancy capacity and it is supposed to be only slowly dispersed by sea currents. As uprooted or otherwise detached plants and shoots soon die, they obviously contribute little to dispersal. Marine mammals and fishes, which feed on the young leaves and fruits, possibly play a role in the dispersal.The seeds of Thalassia hemprichii seem to require a long resting period before they germinate and growth of the seedling is rather slow.Fl. Dec.-Febr., rarely in other months; fr. March-Apr. In Malaysia anthesis is rather rarely observed.