Description from Flora of China
Annual or short-lived perennials. Rhizomes absent. Culms tufted to densely tufted, 5-30 cm tall or more, 0.5-1 mm thick, soft, longitudinally sulcate. Leaf sheaths 2, basally ± purplish and apically green, tubular, 1.5-4 cm, mouth truncate, apex deltoid dentate. Spikelet narrowly ovoid, oblong-ovoid, cylindric, or rarely globose-ovoid, (3-)5-10 × 1.5-3 mm, several to many flowered. Basalmost glume empty, amplexicaul for whole spikelet base; fertile glumes pale rust-colored, ± laxly spirally imbricate, oblong to suboblong, ca. 2 × 1 mm, midvein greenish, margin hyaline, apex obtuse to rounded. Perianth bristles 6, rust-colored, ca. 1.5 × as long as nutlet or slightly shorter, densely or laxly retrorsely spinulose. Stigmas 3. Nutlet yellowish to olivaceous, obovoid, 0.8-1.2 × 0.5-0.7 mm, 3-sided, sides convex, narrowly costate on angles; persistent style base pyramidal to conic, 1/4-1/2 as long and ca. 1/2 as wide as nutlet, sometimes spongy-thickened, apex acuminate. Fl. and fr. Mar-Nov.
Pond margins, shallow ponds, paddy fields, shallow water margins, lake banks; 200-1700 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Liaoning, Shaanxi, Shanxi, Sichuan, Yunnan, Zhejiang [India, Indonesia, Japan, Korea, Malaysia, Myanmar, Philippines, Russia (Far East), Sri Lanka, N Thailand].