Hydrophily is a type of pollination in which pollen is dispersed by the flow of water, especially in rivers and streams. Hydrophilous species fall into two categories:

• Those that distribute their pollen to the surface of water. For example, Vallisnerias male flower or pollen grain are released on the surface of water, which are passively carried away by water currents; some of them eventually reach the female flower.

• Those that distribute it beneath the surface. For example, seagrasses in which female flower remain submerged in water and pollen grains are released inside the water.

Surface pollination is more frequent and appears to be a transitional phase between wind pollination and true hydrophily. In these, the pollen floats on the surface and reaches the stigmas of the female flowers as in Hydrilla, Callitriche, Ruppia, Zostera, and Elodea. In Vallisneria, the male flowers become detached and float on the surface of the water; the anthers are thus brought in contact with the stigmas of the female flowers.

Some examples of hydrophilous flowers are Vallisneria and Hydrilla.