or annual herbs, totally submerged or with floating leaves, in fresh to brakish
water, rootstock creeping, usually rooting at lower nodes. Stems elongated or
shortened, terete to compressed, branched. Leaves simple, alternate, opposite
or whorled, entire, obtuse. Inflorescence a capitate spike, axillary or
terminal, emerged or submerged. Flowers small, bisexual, perianth bractlike, tepals
4, free. Stamens 4, anthers sessile, (1or) 2-celled, extrorse, dehiscent longitudinally. Carpels 4, free, ovule solitary, ovary
superior, styles short, stigmas sessile. Fruits of 4, somewhat compressed
drupelets. Seeds with well-developed embryo, curved, endosperm absent.