Annuals. Roots fibrous. Culms tufted, 10-60 cm tall, slender, compressed triquetrous, smooth, base with several leaves. Leaves shorter than culm; leaf blade 2-5 mm wide, flat, scabrid on apical margin and smooth on other parts. Involucral bracts 3-5, leaflike, basal 2 usually longer than inflorescence. Inflorescence a simple anthela; rays 4-10, mostly to 12 cm, each with 1 spike. Spike broadly ovoid to oblong, 1-3 × 0.8-3 cm, with several to many spikelets. Spikelets laxly arranged, linear to narrowly linear-ovoid, 0.5-1.5 cm × 1-2 mm, obliquely spreading but spreading after anthesis, 8-20-flowered; rachilla wings white, narrow, hyaline, persistent; successive glumes on rachilla ca. 0.5 mm apart. Glumes purplish red to brown on both surfaces but middle green, slightly lax, broadly obovate to suborbicular, 1-1.5 mm, membranous, slightly shiny, 5-veined, midvein forming a keel, apex with an excurved mucro ca. 0.4 mm. Stamens 3; anthers ellipsoid, 0.2-0.4 mm; connective prominent beyond anthers. Style very short; stigmas 3, ± short. Nutlet blackish brown, obovoid to oblong, nearly as long as subtending glume, 3-sided, densely prominently puncticulate, apex mucronate. Fl. and fr. Jul-Oct.

Cyperus amuricus is naturalized in North America.

Grasslands on mountain slopes, seashores, wet places in ditches, river margins, along trails, fields; below 100-2500 m. Anhui, Chongqing, Fujian, N Guangxi, N Guizhou, Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, S Jilin, Liaoning, SE Shaanxi, Shandong, Shanxi, Taiwan, E Xizang, Yunnan, Zhejiang [Japan, Korea, Russia (Far East)].