Aquatic, annual or perennial herbs, submerged or rarely floating. Stipules 0. Flowers unisexual or bisexual, mostly actinomorphic, arranged in a spathe. Perianth tube often present in female and bisexual flowers, usually extending to carry the flower to the water surface. Perianth segments 3 or 6, if 6, differentiated into sepals and petals, sepals and petals free. Stamens 2-many, staminodes often present in female flowers. Ovary inferior, of 2-15 connate carpels, 1(-3)-locular. Styles 2-15. Fruit a capsule.