Plants perennial, of fresh waters. Rhizomes absent; stolons floating on or suspended in water, rooted or not, unbranched, short. Leaves basal, emergent or floating, petiolate; blade elliptic to orbiculate, base reniform or cordate, apex obtuse to acuminate; midvein without rows of lacunae along sides, blade uniform in color throughout, abaxially surface without prickles, smooth on emergent leaves or with aerenchymous tissue on floating leaves; intravaginal squamules entire. Inflorescences cymose, sessile or short-pedunculate; spathe not winged. Flowers unisexual, staminate and pistillate on same plants, emersed, pedicellate; petals greenish white to yellowish. Staminate flowers: filaments connate at least ½ their length; anthers elongate; pollen in monads. Pistillate flowers: ovary 1-locular, falsely 6–9-locular; styles 3–9, 2-fid nearly to base. Fruits ellipsoid to spheric, smooth to ridged, dehiscing irregularly. Seeds ellipsoid, echinate, covered with blunt cylindric hairs.
North America, Central America, South America.
Species 2 (1 in the flora).