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.
Pet broadly obovate, more than 1.5 times as long as the sep; stamens in 4 alternating trimerous whorls (those of the innermost antepetalous whorl staminodial), their filaments connate in pairs below, forming 6 radial pairs; styles usually 6, flat, bifid up to half-length; stipules (1 or) 2, mostly lateral and free from the petiole; roots unbranched; otherwise much like Limnobium. 3, Old World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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