Description from Flora of China
Scirpus atropurpureus Retzius, Observ. Bot. 5: 14. 1788.
Annuals. Rhizomes and stolons absent. Culms greenish, tufted, 2-15 cm tall, hairlike, erect, terete, obtusely longitudinally ribbed. Leaf sheaths 1 or 2, basally purplish red and apically greenish, tubular, 0.5-1.5 cm, mouth obliquely truncate, apex obtuse to acute. Spikelet ovoid, globose, or oblong-ovoid, 2-5.5 × 1.5-2.5 mm, many flowered, apex obtuse. Basal 2 glumes empty; basalmost glume amplexicaul for more than 1/2 of spikelet base; fertile glumes green at middle and blood-red on both sides, laxly imbricate, oblong to elliptic, ca. 1 × 0.5 mm, membranous, midvein obscure, margin narrowly hyaline, apex obtuse to subrounded. Perianth bristles 4(-6), colorless to white, slightly longer to shorter than nutlet, laxly retrorsely spinulose. Stigmas 2. Nutlet at first purplish red then becoming dark purple, obovoid to broadly obovoid, 0.3-0.6 × ca. 0.4 mm, biconvex, smooth and shiny; persistent style base patelliform, umbonate at middle, not reflexed basally, ca. 1/6 as long and ca. 1/4 as wide as nutlet. Fl. and fr. Jun-Oct. 2n = 20.
Rice fields, field margins, moist areas; 200-1400 m. Anhui, Guangdong, Guangxi, Guizhou, Hainan, Hunan, Jiangsu, Shandong, Sichuan, Taiwan, Yunnan [Bhutan, India, Indonesia, Japan, Nepal, Pakistan, Papua New Guinea, Philippines, Vietnam; Africa, Australia, Central, North, and South America, Europe, Indian Ocean islands, Madagascar].