Perennial or rarely
annual, partially or completely submerged aquatic herbs, rarely floating, of
fresh-or salt-water habitats. Leaves basal, or cauline, usually sessile, linear
or orbicular, with or without petioles, often more or less sheathing.
Inflorescence a cyme in especially staminate flowers, or a single flower in
pistillate flowers, bracteates. Flowers bisexual or more commonly unisexual,
small and inconspicuous. Perianth of 3 sepals and 3 white or coloured petals.
Male flowers: stamens 3-many, anthers 2-celled. Female flowers: unipistillate,
ovary inferior, unilocular, style 1, ovules numerous. Fruits berry-like,
globose or linear, dry or fleshy, indehiscent, submerged. Seeds several to
numerous, embryo straight.