Submerged leaves not prickly; leaf blade sagittate or elliptic, 4--10 cm, base deeply cordate. Floating leaves prickly on petioles and along veins; leaf blade abaxially dark purple and adaxially green, to 1.3(--2.7) m in diam., subleathery, abaxially sparsely pubescent, adaxially glabrous, base emarginate or sinuate; veins abaxially strongly ribbed; primary veins prickly on both surfaces. Flower to 5 cm in diam. Peduncle stout, densely prickly. Sepals triangular-ovate, 1--1.5(--3) cm, abaxially dense-ly prickly; prickles retrorse. Petals outer purple-violet fading to inner white, oblong-lanceolate, 1(--2.5) cm. Ovary 7--16-loculed, each locule with 6--8 or more ovules. Fruit dark purple, globose, 5--10 cm in diam., spongy, densely prickly. Seeds black, 8 to many, globose, 6--10 mm in diam.; testa thick, rigid. Fl. Jun--Aug.

This species is cultivated for its starchy seeds.

Lakes, ponds. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Yunnan, Zhejiang [Bangladesh, India, Japan, Kashmir, Korea, Russia (Far East)].