in A. von Humboldt and A. J. Bonpland, Plantae Aequinoctiales 1: 221. 1808.
Herbs, annual. Roots without terminal tubers. Rhizomes slender, short. Leaves erect, terete, with aerenchyma tissue; sheath with ligule free. Inflorescences both scapose and sessile; spikelike racemes or solitary flowers; scapes shorter than leaves, terminated by spikes; spikes racemes with pistillate flowers near base, bisexual medially, staminate proximally; sessile inflorescences 2 or more, with solitary flowers pistillate flower only, 2 or more, sessile. Flowers bisexual and unisexual, to 5 types, sessile; tepals 0–1, green, linear; stamens 0–1; anthers sessile; pistils 1; ovules 1. Bisexual and staminate flowers: tepal present. Pistillate flowers: tepal present, style 0.5–2 mm or tepal absent, style 0.2–30 cm. Fruits nutlets, angular, beaked.
North America, Central America, South America.