(wind pollination) Pollination by pollen carried on the wind. Wind-pollinated flowers often have reduced sepals and petals and often appear before the leaves. This helps ensure that the stigmas are effectively positioned for pollen interception and the stamens are free to release their pollen. The stamens often have very long filaments while the styles may be long and feathery. As female and male parts compete for room they are often found in different flowers on the same plant, as in hazels (Corylus), or on separate plants, as in black bryony (Tamus communis).
The pollen of wind-pollinated plants needs to be light and smooth surfaced and is only released from the anthers on warm dry days. In catkin-bearing species it can be stored in saucer-like bracts until disturbed and transported on a windy day. Wind-transmitted pollen has a typical diameter of 20-30 μm and may be carried thousands of miles but will normally travel less than 1 km. Because air movement is random pollen needs to be produced in vast quantities (a hazel catkin may produce 4 000 000 pollen grains). This is wasteful of the plant's resources and is thought by some to be the most primitive form of pollination. Others consider that the surviving species using this method show evidence of secondary modification from entomophilic forms. Compare entomophily