Description from Flora of China
Cyperus obliquus Nees; C. pilosus var. obliquus (Nees) C. B. Clarke; C. pilosus var. pauciflorus L. K. Dai; C. pilosus var. purpurascens L. K. Dai.
Perennials. Rhizomes with slender stolons. Culms scattered, 25-85 cm tall, stout, acutely triquetrous, smooth or scabrid on angles of apical part. Leaves shorter than culm; sheath brownish, short; leaf blade 6-8 mm wide, flat, margin serrulate scabrid. Involucral bracts 3-5, basal 2 or 3 longer than inflorescence, margin serrulate scabrid. Inflorescence a compound or decompound anthela; rays 3-10, mostly to 14 cm, unequal in length, each with 3-7 raylets broadly triangular in outline. Spikes ovoid to oblong, 2-3 × 1-2 cm, with 10-20 or more spikelets; rachis densely hispid. Spikelets laxly distichous, narrowly linear-ovoid to linear, 2.5-14 × 1-2.5 mm, slightly turgid, spreading, 4-26-flowered; rachilla wings white, narrow, hyaline. Glumes pale, brown, reddish brown, or dark purple on both surfaces but middle green, slightly lax, broadly ovate, 1.8-2.5 mm, thinly papery, 5-7-veined, keel inconspicuous, margin white hyaline, apex mucronate or muticous. Stamens 3; anthers linear-oblong, 0.5-0.8 mm; connective prominent beyond anthers. Style ca. 0.6 mm; stigmas 3, ca. 1 mm. Nutlet nearly black when mature, broadly ellipsoid to obovoid, 1/2-3/5 as long as subtending glume, 3-sided, apex mucronate. Fl. and fr. Aug-Nov. 2n = 36, 68.
Cyperus pilosus is naturalized in North America.
Sparse forests, forest margins, grasslands on slopes, marshes, meadows, river margins, wet places, paddy fields, water margins, along trails, parks; near sea level to 2100 m. Anhui, Chongqing, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangsu, Jiangxi, Shanxi, Sichuan, Taiwan, SE Xizang, Yunnan, Zhejiang [Bangladesh, Bhutan, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; N Autralia, Pacific islands].