Description from Flora of China
Stems 10-20 cm tall, 0.5-1 mm in diam. Leaves narrowly linear to linear, 1-2.5 cm × 0.4-1 mm; sheath 1.5-3 mm, deeply auriculate; auricles narrowly triangular or lanceolate, 1-2 mm, serrulate with several teeth on each side, apex acute; leaf margin minutely and densely serrulate with 30-50 inconspicuous teeth on each side, consisting of brownish spine cells only. Plants monoecious; flowers solitary, or sometimes 2 or 3 together. Male flowers usually more toward upper axils, ca. 1 mm, elliptic; spathe absent; anther 4-thecous. Female flowers 1.5-2 mm; style ca. 1 mm; stigmas 2-4-lobed. Fruit oblong, 1.5-2 × ca. 0.8 mm. Seeds ellipsoid-oblong, with ca. 30 rows of pits; areoles hexangular and irregularly polygonal toward ends, or rectangular. Fl. and fr. Jun-Sep. 2n = 12*, 24, 36*, 48, 72.
Ponds, paddy fields, usually in still or slow-moving water; below 1800 m. Anhui, Fujian, Guangdong, Guangxi, Hainan, Hebei, Henan, Hubei, Jiangsu, Liaoning, Sichuan, Taiwan, Yunnan, Zhejiang [Afghanistan, Bangladesh, India, Indonesia, Japan (including Ryukyu Islands), Kazakhstan, Korea, Malaysia, Myanmar, Nepal, New Guinea, Pakistan, Philippines, Sri Lanka, Tajikistan, Thailand, Uzbekistan, Vietnam; Africa, SW Asia, Australia, Europe; introduced in North America].