Aquatic perennial, sometimes behaving as an annual or a biennial; culms spongy, 40-150 cm high, decumbent and rooting at the nodes. Leaf-blades 8-50 cm long, 6-10 mm wide; ligule a line of hairs; sheaths glabrous. Inflorescence narrowly lanceolate, rarely narrowly ovate, 7-20 cm long, typically ± open with the racemes secund and usually ascending; racemes simple, 2-6.5 cm long, coarsely spiculate. Spikelets ovate to broadly ovate or rounded, 3.5-5 mm long, pubescent to hispid, often from tubercles; lower lemma tapering to an awn up to 10 mm long; upper lemma 34 mm long.