Description from Flora of China
Annuals. Roots fibrous. Culms tufted, 3-30 cm tall, flaccid, compressed triquetrous, smooth, base clothed with a few bladeless sheaths, apical sheaths with short blade. Leaves shorter than culm, 2-3 mm wide, flat; sheath reddish brown to purplish brown, 2-6 cm. Involucral bracts usually 2(or 3), leaflike, usually basalmost equaling or longer than inflorescence. Inflorescence a compound or sometimes simple anthela; rays 4-10, mostly to 7 cm, unequal in length, each with 2-9 raylets. Spikelets 3-12, digitately arranged at apex of raylets or rays, linear, 3-12 × ca. 1 mm, 10-40-flowered; rachilla wingless. Glumes dark brown on both surfaces but middle abaxially yellowish green, lax, elliptic to suboblong, 0.8-1 mm, membranous, slightly spreading after anthesis, veins inconspicuous, apex obtuse to truncate, slightly excurved, and muticous. Stamens 1 or 2; anthers not setose at apex. Style long; stigmas 3. Nutlet yellowish, obovoid, ca. 0.3 mm, tuberculate. Fl. and fr. Sep-Nov. 2n = 16.
Cyperus tenuispica is naturalized in Central and South America.
Sparse forests, along trails, wet places, paddy fields; below 100-500 m. Anhui, Guangdong, Guangxi, Guizhou, Hainan, Hunan, Jiangsu, Jiangxi, Sichuan, Taiwan, SE Xizang, Zhejiang [Bhutan, India, Indonesia, S Japan, Kashmir, Korea, Laos, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Tajikistan, Thailand, Uzbekistan, Vietnam; tropical Africa, Australia, Indian Ocean islands].