ectohydrophily

Ectohydrophily is a form of hydrophily, the water-mediated pollination observed in some aquatic plants. In ectohydrophily, pollen is dispersed on the surface of the water and encounters stigmas that are exposed at or near the air–water interface. Pollen grains and stigmas are adapted to interact at the surface, with pollen often buoyant or coated with mucilage to remain at the interface.

This mode of pollination relies on surface processes such as water currents, wind-driven movement, and pollen that can persist at the water’s surface long enough to reach a receptive stigma. It contrasts with submerged or fully underwater pollination, where pollen is transferred to stigmas beneath the water surface. The terminology and distinctions among surface-based and submerged forms of hydrophily can vary among authors.

Ectohydrophily tends to occur in environments that maintain a stable surface film and moderate surface movement. It is relatively uncommon among aquatic angiosperms, reflecting specialized ecological conditions and plant adaptations. The ecological and evolutionary significance lies in how plants optimize pollen dispersal when fully submerged pollination is limited by water movement, pollen viability, and timing of stigma receptivity.

In summary, ectohydrophily describes surface-based water pollination where pollen and stigmas meet at the air–water interface, illustrating one of several specialized strategies aquatic plants employ to achieve fertilization.