Description from Flora of China
Annuals. Roots fibrous. Culms tufted, 2-65 cm tall, slightly thick or flaccid, compressed triquetrous, smooth, few leaved at basal part. Leaves shorter than culm; sheath brown, slightly long; leaf blade 2-6 mm wide, flat or folded. Involucral bracts 2(or 3), leaflike, longer than inflorescence. Inflorescence a simple or rarely compound anthela; rays 3-9, mostly to 3(-5) cm, unequal in length, each with many spikelets at apex densely aggregated into a capitulum. Capitulum of spikelets globose, 0.5-1.5 cm in diam. Spikelets narrowly ovoid to linear, 2-8 × 1-1.2 mm, compressed orbicular, 8-28-flowered; rachilla wingless. Glumes dark reddish purple to dark grayish brown on both surfaces but middle yellowish, less than 1 mm, slightly spreading, obscurely 3-veined, margin white hyaline, apex rounded. Stamens (1 or)2; anthers ellipsoid; connective not prominent beyond anthers. Style very short; stigmas 3, short. Nutlet yellowish, obovoid-ellipsoid, nearly as long as subtending glume, 3-sided. Fl. and fr. Jul-Oct. 2n = 18, 28, 32, 34, 36.
Cyperus difformis is naturalized in Central, North, and South America.
Grasslands at mountain slopes, shallow water, water margins, lake margins, wet places in grasslands, along trails, paddy fields; below 100-2000 m. Anhui, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Yunnan, Zhejiang [Afghanistan, Bangladesh, Bhutan, India, Indonesia, Japan, Kashmir, Kazakhstan, Korea, Kyrgyzstan, Malaysia, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Russia, Sri Lanka, Tajikistan, Thailand, Uzbekistan, Vietnam; Africa, SW Asia, Australia, Europe, Indian Ocean islands, Madagascar, Pacific islands].