Anemophilous flowers are those flowers whose pollens are transferred by wind from the anthers to the stigmas of the same or a different plant. Here are some of the characteristic features of anemophilous flowers that have been identified by botanists:
- They are often small and inconspicuous and are usually developed well before the foliage, so that this does not interfere with the free circulation of air around the flowers.
- They do not develop nectarines nor are they scented.
- The male parts tend to produce very large quantities of pollen by comparison with entomophilous flowers. This compensates for the indirect and somewhat risky means of transport. The greater the quantity of pollen, the greater are the chances of pollination. The aggregation of many male flowers into flexible catkins is common among trees, and clouds of pollen can be seen as it is shed from the hazel, oak and other trees.
- The stigmas are often large, feathery and very sticky, and extend well outside the flower. Thus the pollen is more likely to reach them.
- To remain airborne as long as possible, the pollen grains are usually very tiny, smooth-walled, dry and light; sometimes they have air-bladders.
- Plants with anemophilous flowers are either trees or herbaceous plants with flowers high above the foliage. Thus there is less interference with pollen dispersal or pollen capture by the stigmas.
Some aquatics are pollinated by water currents, e.g the grass wrack, Zostera marina, in which the long thread-like pollen grains, whose specific gravity is the same as that of sea water, are able to move freely at any depth until caught on the submerged feathery stigmas of the female flowers. Some land plants rely on animals other than insects. Humming birds feeding on nectar are said to pollinate many tropical flowers. Creeping animals, such as slugs and snails, must pick up pollen in their slime when moving over plants and may conceivably deposit it on the stigma. There is little doubt that many animals may disperse pollen in one way or another, but flowering plants generally have evolved so that they are well adapted to insect or wind pollination.
Interestingly, it is worthy of note that some flowering plants never fully open their flowers and are habitually self-pollinated, e.g. wood sorrel. They are said to be cleistogamic. Others have evolved very highly specialized pollination mechanism such as the explosive properties of flowers of some leguminous plants and the development of hinged anthers as in the sage.