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 solitary in each cell, pendulous from the top of the cavity. Styles 2, free, often long, papillose. Fruit 4-lobed, with longitudinally margined or winged lobes. Testa membranous; endosperm fleshy; embryo terete, straight. Distr. Only genus in the family, worldwide distributed, not yet known from S. Africa and in various regions scarce, in Malaysia apparently very rare, the only record proving its being indigenous is from the New Guinean highlands. Because of their small size terrestrial forms are easily overlooked.