The agents responsible for pollination in angiosperms have been grouped into two main categories:
Adaptation for Wind Pollination or Anemophily:
- Flowers are small, colourless, inconspicuous, nectar less and become arranged as inflorescence.
- The anthers are well exposed for the easy dispersal of pollen grains.
- Pollen grains are small, light, dry, dusty, non-sticky and sometimes even winged.
- The stigmas are large, hairy and feathery or branched to catch the airborne pollen grains.
- Pollen grains are produced in a large number so that they can be spread to a large area covering maximum flowers.
- Common examples of wind-pollinated flowers are grass, sugarcane, bamboo and coconut, etc.
Adaptation for Water Pollination:
- Water pollination is also termed as hydrophily and mode of pollination is water.
- It is quite rare in flowering plants and is limited to about 30 genera, mostly monocotyledons.
- It is very common in plant groups such as algae, bryophytes and pteridophytes.
- Flowers are small, colourless, inconspicuous, odourless and nectar-less and pollen grains and stigmas are generally unwettable.
- The stigmas are long and sticky, e.g., Vallisneria, Hydrilla and Zostera.
- Not all aquatic plants use water for pollination. In a majority of aquatic plants, the flowers emerge above the level of water and are pollinated by insects or wind as in land plants, e.g., water hyacinth and lily.
- In Vallisneria, the female flower reaches the surface of the water by the long stalk and pollen grains are released on to the surface of the water. They are then carried by the passive water currents.
- In most of the water pollinated species, pollen grains are protected by mucilaginous covering.