Hydrophily

Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams.

In these the pollen floats on the surface and reaches the stigmas of the female flowers as in Hydrilla, Callitriche, Ruppia, Zostera, Elodea.

[2] Species exhibiting true submerged hydrophily include Najas, where the pollen grains are heavier than water, and sinking down are caught by the stigmas of the extremely simple female flowers,[1] Posidonia australis or Zostera marina[3] and Hydrilla.

Hydrophily is unique to obligate submersed aquatic angiosperms with sexually reproductive parts completely submerged below the water surface.

True hydrophily occurs in 18 submersed angiosperm genera, which is associated with an unusually high incidence of unisexual flowers.