Posidonia australis Hook.F.

Rhizomes laterally compressed, 5–15 mm thick; internodes 1–4 cm long, covered with fibrous remains of sheaths. Leaves 2–4 per shoot. Leaf sheath 6–10 cm long, with margins overlapping for ⅓ its length, becoming a hair-like mass after blade is shed; ligule 1–1.5 mm long; auricles 3–4 mm long. Leaf blade flat, linear, slightly curved, 20–140 cm long, 6–20 mm wide; apex rounded to truncate; longitudinal veins 14–20; epidermal cells isodiametric with smooth margins, l:w 0.5–1; fibre bundles associated more with epidermis than hypo-dermis. Inflorescence of 2–5 spikes, each with 2–6 flowers; peduncle 15–60 cm long. Anther 4–5 mm long, 1.2 mm diam.; anther connective 4–5 mm long. Ovary 2–3 mm long, 1.5 mm diam.; stigma 1.7–3 mm high, irregularly papillose with 2 or 3 crests. Fruit asymmetrically laterally compressed, oblong to ellipsoid, 2–3 cm long. Seed ellipsoid, 15–25 mm long.

Grows from low tide mark to 15 m deep in sheltered bays and estuaries and forms extensive meadows where it is often associated with other Posidonia, Amphibolis and Heterozostera. 

Can be grown by seedlings.