Plants perennial, rarely annual, submersed, floating-leaved, or emersed, glabrous to sparsely pubescent; rhizomes often present, occasionally terminated by tubers; stolons often present; corms absent; tubers white to brown, smooth. Roots septate. Leaves sessile or petiolate; petiole terete to triangular; blade with translucent markings absent, linear to obovate, base attenuate to hastate or sagittate, margins entire, apex round to acute. Inflorescences racemes, panicles, rarely umbels, of 1--17 whorls, erect, emersed or floating, rarely submersed; bracts coarse or delicate, apex obtuse to acute, smooth or papillose proximally to distally. Flowers unisexual, the proximal rarely with ring of sterile stamens; staminate flowers pedicellate, distal to pistillate flowers; pistillate flowers mostly pedicellate, rarely sessile; bracts subtending pedicels, lanceolate, shorter than pedicels, apex obtuse to acute; pedicels ascending to recurved; receptacle convex; sepals recurved in staminate flowers, recurved to erect in pistillate flowers, often sculptured, herbaceous to leathery; petals white, rarely with pink spot or tinge, entire; stamens 7--30; filaments linear to dilated, glabrous to pubescent; pistils to 1500 or more, spirally arranged, not radiating in starlike pattern, distinct; ovules 1; styles terminal. Fruits without longitudinal ribs, compressed, abaxially keeled or not, abaxial wings often present, lateral wing often present, 1, curved, glands present. x = 11.