Delicate, annual or perennial herbs, aquatic and then either entirely submersed, or floating in the upper part, or, in humid localities, not rarely terrestrial and creeping, with slender stems. Leaves opposite, at the summits of floating stems often spuriously rosulate, exstipulate, small, linear, elliptic, oblong or spathulate, entire, herbaceous, in the Mal. sp. triplenerved. Flowers minute, unisexual, axillary, solitary or rarely one ♂ and one ♀ flower from the same axil, often with 2 caducous, transversal, opposite, tender concave bracts. Calyx and corolla absent, ♂: Stamen 1; filament thin, anther 2-celled, cells bursting lengthwise, the slits becoming confluent at the top. ♀: Ovary sessile or subsessile, 4-lobed, 4-celled. Ovule solit...