Stems 30-100 cm or more tall, 1-4.5 mm in diam., mostly armed with spines, spines sometimes absent except apically. Leaves 1.5-3 cm × 2-3.5 mm, fleshy, abaxial side of midvein usually with spines; sheath ca. 3 mm, entire or serrulate with 1-3 spine cells on upper side without auricle, leaf acute at apex, with 2-10 conspicuous teeth on each side of margin; teeth 1-2 mm. Plants dioecious; flowers yellowish green. Male flowers ca. 5 × 2 mm; spathe with a short neck; anther 4-thecous. Female flowers 2-4.5 mm; style ca. 1 mm; stigmas 2- or 3-lobed. Fruit elliptic to obovoid-elliptic, 4-6 × 3-4 mm. Seeds ovoid; testa pitted; areoles polygonal, irregularly arranged. Fl. and fr. Sep-Nov. 2n = 12*, 24, 48, 60*.

Ponds, lakes, slow-moving rivers; below 2700 m. Anhui, Guangdong, Guangxi, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Shandong, Shanxi, Taiwan, Xinjiang, Yunnan, Zhejiang [India, Japan, Kazakhstan, Korea, Kyrgyzstan, Malaysia, Mongolia, Myanmar, Pakistan, Russia, Sri Lanka, Tajikistan, Turkmenistan, Uzbekistan, Vietnam; Africa, SW Asia, Australia, Europe, North and South America].