Ischaemum involutum G. Forster, Fl. Ins. Austr. 73. 1786; Thuarea latifolia R. Brown; T. media R. Brown; T. sarmentosa Persoon.

Culms long and creeping, much branched, rooting at nodes, flowering culms up to 20 cm tall. Leaf sheaths loose, imbricate on the short erect shoots, pilose or only ciliate along margins; leaf blades 2–5 × 0.3–0.8 cm, usually puberulous on both surfaces; ligule 0.5–1 mm. Inflorescence a terminal raceme, not exserted from the uppermost spathelike leaf sheath; rachis broad and winglike in lower fertile part, narrowed above in staminate part. Spikelets pubescent; staminate spikelet oblong-lanceolate, 3–4 mm; fertile spikelet ovate-lanceolate, 3.5–4.5 mm. Fl. and fr. Apr–Dec.

The short flowering shoots bend down as the seed ripens, and the seed may become buried in the sand. The plant is an efficient sand binder, and the prostrate, rooting stems form widely spreading mats. With its curious, watertight, buoyant fruit-case, this grass is also adapted to long-distance dispersal by sea.

The combination Thuarea involuta has often been attributed to Roemer & Schultes (Syst. Veg. 2: 808. 1817), but this was not published until November 1817, whereas Smith published in May of that year.

Sandy seashores. Guangdong, Hainan, Taiwan [Indonesia, Malaysia, New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; Australia, Indian Ocean Islands, Madagascar, Pacific Islands (Polynesia)].