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.
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.
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.
Fls unisexual, the plants monoecious; spathes basal and sessile or short-pedunculate, the staminate 1-lvd and subtending 2-9 fls, the pistillate 2- lvd and usually subtending a solitary fl; fls long-pedicellate; sep 3; pet 3, narrow, not more than ca 1.5 times as long as the sep, or wanting; filaments united into a central column, from which the 9-12(18) anthers diverge in the upper half; ovules scattered over the surfaces of the 6-9 deeply intruded (or axially joined?) parietal placentas; styles 6-9, bifid nearly to the base, each cleft into 2 linear, hairy lobes; fr fleshy, many-seeded; aquatic or marsh herbs, rooting and producing tufts of lvs at the nodes of the long stolons, or in deeper water occasionally free- floating; lvs with long petiole and floating or emergent, dilated blade; stipule 1, axillary, adnate below to the petiole; roots usually with numerous simple branches. Monotypic.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.