Description from Flora of China
Trapa bispinosa Roxburgh var. incisa (Siebold & Zuccarini) Franchet & Savatier; T. incisa var. quadricaudata Glück; T. maximowiczii Korshinsky; T. maximowiczii var. tonkinensis Gagnepain; T. natans Linnaeus var. incisa (Siebold & Zuccarini) Makino.
Stem 1-2.5 mm in diam. Petiole 5-15 cm, slender, slightly swollen distally or not; leaf blade glossy and dark green adaxially, green or sometimes purplish abaxially, often black-brown or with 2 dark spots basally, rhombic-triangular, 1.5-3 × 2-4 cm, glabrous or sparsely pubescent on veins, adaxially glabrous, base broadly cuneate, margin coarsely and sharply incised-dentate distally. Petals pink to pale purplish or white, 5-7 mm. Fruit narrowly rhombic, 0.8-1.5 × 1.2-2 × 0.7-1 cm, 4-horned, surface variously ribbed to smooth, crest absent, crown dome-shaped to inconspicuous, 1-3 mm, beak finely conic; horns conic, 1-1.5 cm, unequal, lower horns descending, upper horns horizontal to ascending, apex barbellate. Fl. May-Oct, fr. Jul-Nov. 2n = 48, 88*, 90*, 92*, ?96.
Swamps, ponds; near sea level to 1000 m, to 2000 m in SW China. Anhui, Fujian, Guangdong, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Shaanxi, Sichuan, Taiwan, Yunnan, Zhejiang [India, Indonesia, Japan, Korea, Laos, Malaysia, Russia (Far East), Thailand, Vietnam].