Annuals or perennials, rooting in mud. Vegetative stem submersed and growing to surface or short and growing in mud; flowering stem submersed or emersed, glabrous, slightly constricted just below first node. Sessile leaves submersed, forming a basal rosette, thin, acuminate to acute at apex; petiolate leaves floating or emersed, cordate to reniform, thin or thickened, obtuse to acuminate at apex. Inflorescence a spike, developing over several days, the peduncle glandular-pubescent or pilose when emersed, subtending spathe folded with an acute apex. Flowers with perianth funnelform, the tepals evenly spaced around central axis, oblong, glandular-pubescent or pilose on adaxial surface, obtuse to acuminate at apex; stamens 6, the 3 upper ones shorter than the 3 lower ones, filaments glandular-pubescent, anthers ovoid to oblong; carpels 3, but only one developing to maturity, containing a single ovule, placentation basal; tristylous or homostylous. Fruit a nutlet; the perianth thickened, with spinulose longitudinal ridges; seed ovoid, smooth.