Description from Flora of China
Herbs, perennial or annual, rhizomatous or not; stolons sometimes present. Culms erect, 3-angled or rarely terete. Leaves cauline or both basal and cauline; sheaths at middle part of culm, winged or not, apex sometimes with contraligule opposite blade; leaf blade linear, scabrid, sheathing, usually prominently 3-veined. Involucral bracts leaflike and sheathing, setaceous, or glumelike; bractlets usually setaceous, rarely glumelike. Inflorescences terminal, paniculate, usually stout and elongated, sometimes reduced into a discontinuous spike. Unisexual spikelets usually dominant on inflorescence, rarely bisexual ones dominant; basal 2-4 glumes of spikelets empty. Male spikelets with several flowers. Female spikelets with a single flower. Bisexual spikelets with a basal female flower and several male flowers. Flowers unisexual. Male flowers: stamens 1-3; anthers linear or linear-oblong; connective apex often protruding and subulate. Female flowers: style base not inflated; stigmas 3. Nutlet brick red, white, or yellowish purple, spherical or ovoid, often obtusely 3-sided, smooth or variously sculptured, mostly shiny, glabrous or hairy (hairs simple or stellate), usually borne on a gynophore apically dilated into a ± 3-lobed disk.
Note: nutlets and underground parts are essential for accurate identification.
About 200 species: pantropical and extending into temperate regions in S Africa, E Asia, and North and South America; 24 species (three endemic) in China.
(Authors: Zhang Shuren (张树仁); Gordon C. Tucker, David A. Simpson)