Sp. Pl. 2: 1036. 1753; Gen. Pl. ed. 5; 458, 1754.
Plants perennial, of fresh waters. Rhizomes absent; stolons present. Stems floating on or suspended in water, rooted or not, unbranched, short. Leaves basal, emergent or floating, petiolate; blade cordate to reniform or orbiculate, base reniform or cordate, apex obtuse to almost truncate; midvein without rows of lacunae along sides, uniform in color throughout, abaxial surface without prickles, smooth on emergent leaves or with aerenchymous tissue on floating leaves; intravaginal squamules entire. Inflorescences 1-flowered or cymose, sessile or short-pedunculate; spathe not winged. Flowers unisexual, staminate and pistillate on different plants [on same plants], emersed, pedicellate; petals white to pinkish. Staminate flowers: filaments distinct or basally connate, distinct portion longer than connate; anthers oval; pollen in monads. Pistillate flowers: ovary 1-locular; styles 6, 2-fid less than ½ length. Fruits spheric, smooth to ridged, dehiscing irregularly. Seeds ellipsoid, minutely tuberculate or muricate.
Introduced; North America, Eurasia, Africa, Australia.
Species 3 (1 in the flora).