HYDROCHARITACEAE, in botany, a family of mono cotyledons, belonging to the series Helobieae. They are water plants, represented in Britain by frog-bit (Hydrocharis Morsus ranae) and water-soldier (Stratiotes aloides). The family contains about 5o species in 13 genera, I o of which occur in fresh water while 3 are marine : and includes both floating and submerged forms. Hydrocharis floats on the surface of still water, and has rosettes of kidney-shaped leaves, from among which spring the flower-stalks; stolons bearing new leaf-rosettes are sent out on all sides, the plant thus propagating itself in the same way as the strawberry. Stratiotes aloides has a rosette of stiff, sword-like leaves, which project above the surface when the plant is in flower. It is stoloniferous, the young rosettes sinking to the bottom at the beginning of winter and rising again to the surface in the spring. Vallisneria (eel-grass) contains two species, one native of tropical Asia, the other inhabiting the warmer parts of both hemispheres and reaching as far north as south Europe. It grows in the mud at the bottom of fresh water, and the short stem bears a cluster of long, narrow, grass-like leaves. New plants are formed at the end of horizontal runners. Another type is represented by Elodea canadensis or water-thyme, which has been introduced into the British Isles from North Amer ica. It is a small, submerged plant with long, slender, branch ing stems bearing whorls of nar row, toothed leaves; the flowers appear at the surface when mature. In Hydrocharis, a dioe cious plant, the flowers are borne above the surface of the water, have conspicuous white petals, contain honey and are pollinated by insects. Stratiotes has similar flowers which come above the surface only for pollination, be coming submerged again during ripening of the fruit. In Vallis neria which is also dioecious, the small male flowers are borne in large numbers in short-stalked spathes ; the petals are minute and scale-like, and only two of the three stamens are fertile; the flowers become detached before opening and rise to the surface, where the sepals ex pand and form a float bearing the two projecting semi-erect stamens. The female flowers are solitary and are raised to the surface on a long, spiral stalk; the ovary bears three broad styles, on which some of the large, sticky pollen-grains from the floating male flowers get deposited. After pollination the female flower is drawn below the surface by the spiral contraction of the long stalk, and the fruit ripens near the bottom.
The family is a widely distributed one; the marine forms are tropical or subtropical, but the fresh-water genera occur also in the temperate zones. In addition to the water-thyme (Elodea), found across the continent, and the eel-grass (Vallisneria), of the eastern States and Canada, the family is represented in North America by the American frog-bit (Limnobium Spongia), of the southeastern States, and the marine Halophila Engelmannii, of the Florida coast.