A genus of water plants with creeping, sympodial rhizomes and erect, leafy branches, which are chiefly confined to fresh water. The leaves are alternate, simple or entire, and either all submerged or with some floating. Those with floating leaves tend to have broader leaves, while those with all the leaves submerged tend to have narrow leaves. This is believed to form a series in evolutionary terms from land-based to truly aquatic plants. The flowers are axillary or terminal spikes, and are inconspicuous. The parts are in fours. The fruit is a small, green to brown drupe or achene containing seeds. These seeds have no endosperm but contain air, allowing the fruit to float. The plants overwinter as the complete plant, or die back to the rhizome, or form special branches with tubers or winter buds. There are about 90 species, found throughout the world in a variety of aquatic habitats. Most species are edible, and provide food for many animals.
Subjects: Plant Sciences and Forestry.