Rhizomatous and stoloniferous aquatic or semi-aquatic perennial. Stems ascending forming loose, floating mats in water to 1 m deep or more, or with culms to 50 cm high when not submerged; nodes hairy. Leaves glabrous, sometimes lightly scabrous; blade flat, 4–12 cm long and 2–7 mm wide, midrib prominent on lower surface; ligule membranous, erose, 1–4 mm long. Panicle pyramidal, 3–15 cm long, lower branches spreading, 3–7 cm long, flexuose. Spikelets sub-sessile, narrow-lanceolate, mostly 4–7 mm long; lower glume broad, truncate, 0.5–1 mm long, papery, apparently nerveless; upper glume as long as the spikelet, 9–11-nerved, scabrous to spinose along the nerves; lemma of lower (male) floret smooth, from two-thirds to three-quarters as long as upper glume, its palea slightly shorter; lemma of upper (female) floret acute, c. 1.5 mm long, membranous, almost completely enclosing floret, palea subequal to lemma. Flowers Oct.–Apr.
MuM, Wim, VVP, VRiv, MSB, RobP, MuF, Gold, CVU, DunT, NIS. All mainland states. ?Asia, Indonesia, New Guinea. Locally common in and near lakes, lagoons and slow-flowing streams in northern Victoria along the Murray River and its tributaries downstream from about Corowa, and scattered occurrences in the west (e.g. Glenelg River at Cherrypool, Lake Lonsdale near Stawell). An 1899 collection labelled 'Hawkesdale' is doubtfully from that location.
