Citation: Cambridge & Kuo, Aquatic Bot. 20:285 (1984).

Synonymy: P. aff. ostenfeldii E. Robertson in H. B. S. Womersley, Marine benthic fl. southern Aust. 85 (1984), partly. , Posidonia aff. ostenfeldii Hartog, Posidonia ostenfeldii

Common name: None

Description:
Robust rhizomatous perennial marine herb; rhizomes somewhat compressed, more or less elliptic in cross section, 2-5 mm thick, internodes variable in length, frequently an elongate internode up to 10 cm long alternating with a series of much shorter internodes 0.5-2.5 mm long; roots arising irregularly, 1 or 2 per node, frequently pale-brown to reddish-brown in colour, 1-4 mm diam., with a few line laterals, becoming hollow with age; leaves 2 or 3 per shoot; sheath 8-20 cm long, with margins overlapping for about three-quarters of the length; ligule c. 1 mm long; auricles c. 2 mm long, mostly dark-brown; the abscission line between the blade and the sheath usually conspicuous; after fall of the blade the sheath disintegrates into numerous pale-yellow to grey hair-like fibres; blade usually 40-125 cm (sometimes to 1.9 m) long, 2.5-8 mm broad, biconvex in cross section, longitudinal vascular bundles 7-11 (clearly seen in cross section of the blade, but inconspicuous in the surface view, except near the apex); apex somewhat flattened, usually spathulate with slightly recurved margins, occasionally rounded.

Inflorescence on a flattened peduncle 25-65 cm long, usually much shorter than the foliage leaves, subtending bracts 2, unequal, the longer up to 30 cm; spikes 4-8, each terminating in a spur; flowers usually 3 or 4 per spike; stamens 3, connective 5-8 mm long, linear-lanceolate, with a shallow keel; ovary c. 5 mm long, oblong-ellipsoid; stigma lobes 3, irregularly verrucose.

Fruit 3-4 cm long, more or less ellipsoid, somewhat falcate.

Published illustration: Robertson in Womersley (1984) Marine benthic flora southern Aust., figs 2lB, 22N-Z & 23.

Distribution:  From the uppermost sublittoral to 22 m deep, in pure stands or in association with other seagrasses, mostly in areas of strong wave action. S.Aust.: NU, EP, YP, SL, KI, SE.   W.Aust. Conservation status: native Flowering time: Flowering and fruiting: Nov. — Jan.

SA Distribution Map based on current data relating to specimens held in the State Herbarium of South Australia

Biology: No text

Author: Not yet available