Perennial aquatic with stout rhizome. Culms terete, transversely septate, to 5 m high (in deep water), to c. 1.5 m above water, 4–12 mm diam. Spikelet terete, tapering to apex, 3–5 cm long, 8–9 mm diam., glumes ± obtuse, finely striate with a fairly prominent midrib and narrow hyaline margins, straw-coloured, usually with dark reddish band near margins, 7–11 mm long; hypogynous bristles 8–10, reaching at least to top of the style-base, sparsely but regularly toothed, united at the base; stamens 3; anthers 3–5 mm long; style 3-fid. Nut turgidly biconvex, with angles not ribbed, obovoid to orbicular, straw-coloured to dark golden brown, 2–2.7 mm long, 1.8–2.5 mm diam., external cells irregularly isodiametric, often elongated vertically in no regular series; style-base from one-half as long as to equalling and about two-thirds as wide as nut. Flowers spring–summer.