Coarse herb, to 1.5 m tall, usually aquatic; culms triangular. Leaves linear, to 1 m long, l-2 cm wide, the midrib scabrous on the underside, the margins scabrous. Dense corymbs arising from each of the upper leaves, to 12 cm long, the bracts caudate-acuminate, the upper flowers staminate, the lower flowers bisexual; spikelets numerous, brown at maturity, 7 mm long, containing a single achene; scales thin, brown, glabrous, the keel green; stamens 3; style bifid. Achenes 2-3 mm long, obovate, brown, with corky conic beak, the bristles exceeding achene. Croat 13981.