Cyperus sanguinolentus Vahl, Enum. Pl. 2: 351. 1805, nom. cons.; C. eragrostis Lamarck var. cyrtostachys Miquel; C. eragrostis var. humilis Miquel; C. eragrostis f. melanocephalus (Miquel) J. V. Suringar; C. flavescens Linnaeus f. rubromarginatus Schrenk; C. korshinskii Meinshausen; C. melanocephalus Miquel; C. sanguinolentus f. humilis (Miquel) Kükenthal; C. sanguinolentus f. melanocephalus (Miquel) Kükenthal; C. sanguinolentus f. rubromarginatus (Schrenk) Kükenthal; Pycreus korshinskii (Meinshausen) V. I. Kreczetowicz; P. sanguinolentus var. cyrtostachys (Miquel) L. K. Dai; P. sanguinolentus f. humilis (Miquel) L. K. Dai; P. sanguinolentus f. melanocephalus (Miquel) L. K. Dai; P. sanguinolentus f. rubromarginatus (Schrenk) L. K. Dai.

Annuals. Roots fibrous. Culms densely tufted, 5-50 cm tall, compressed 3-angled, smooth, with several leaves basally. Leaves several, usually shorter than culm to rarely longer; sheath usually reddish brown, short; leaf blade 2-4 mm wide or less, flat, apical margin denticulate. Involucral bracts 2-5, leaflike, longer than inflorescence, subspreading. Inflorescence a simple anthela; rays 3-5, mostly to 4.5 cm to sometimes very short and inflorescence a capitulum, each with 4-12 or more spikelets congregated into a short spike or nearly a capitulum. Spikelets radially spreading, narrowly ovoid to narrowly oblong-ovoid, 0.5-1.8 cm × 2.5-3 mm, 6-24-flowered; rachilla straight, 4-angled, wingless. Glumes straw-colored, brownish yellow, or blackish brown on both surfaces but middle yellowish green, slightly laxly imbricate, ovate, ca. 2 mm, membranous, medially 3-5-veined, often distinctly furrowed on both sides of keel, margin dark blood-red to dark brownish red, apex obtuse. Stamens (2 or)3; anthers linear, 0.7-1 mm. Style long; stigmas 2, exserted, slender. Nutlet black at maturity, globose-obovoid to broadly ellipsoid, 1-1.3 mm, 1/2-3/5 as long as subtending glume, biconvex, slightly turgid, minutely punctate. Fl. and fr. Jul-Dec. 2n = 48, 50.

Pycreus sanguinolentus is naturalized in North America.

Sparse forest margins, grasslands on mountain slopes, meadows, swamps, lake margins, sunny places at river margins or shallow water, valleys, wet places along trails, field margins, old fields; below 100-3400 m. Anhui, Chongqing, Fujian, S Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, S and SE Xizang, Yunnan, Zhejiang [Bhutan, India, Indonesia, Japan, Kashmir, Kazakhstan, Korea, Kyrgyzstan, Malaysia, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Russia, Sri Lanka, Tajikistan, Thailand, Turkmenistan, Uzbekistan, Vietnam; Africa, SW Asia, Australia, Pacific islands].