Pollination through water is an uncommon phenomenon in flowering plants and occurs in only about 30 genera, primarily among monocotyledons.
However, in lower plant groups like algae, bryophytes, and pteridophytes, water is a regular medium for transporting male gametes. It is believed that the distribution of some plants, particularly some bryophytes and pteridophytes, is limited because of their dependency on water for the transportation of male gametes.
Vallisneria and Hydrilla, which grow in fresh water and several marine sea-grasses such as Zostera are some common examples of water pollinated plants.
It is not that all aquatic plants use water for pollination. In a majority of aquatic plants such as water hyacinth (Eichhornia) and water lily (Nymphea), the flowers rise above the water’s surface and are pollinated by insects or wind, similar to terrestrial plants.
However, some aquatic plants have adaptations to water pollination. In Vallisneria, the female flower reaches the surface of water by the long stalk, while the male flowers or pollen grains are released on to the surface of water. The water currents carry these pollen grains passively; some of them eventually reach the female flowers and the stigma, leading to fertilization.
In another group of water pollinated plants such as seagrasses (Zostera), the female flowers remain submerged in water. Their pollen grains are released directly into the water. Pollen grains in many such species are long, ribbon like and are carried passively inside the water; some of them reach the stigma and achieve pollination.
Pollen grains, in most of the water-pollinated species, are protected from wetting by a mucilaginous covering. The flowers which are pollinated by water lack scent and nectar.
Here we must remember the fact that if a plant is producing attractive, colourful flowers with a smell (pleasant or unpleasant) and nectar, are pollinated by animals. Insects are the most common animal pollinators.
Name: Mukesh Verma
Department: Botany NEET
Narayana Jaipur Center (NIHQ)