Pollination occurs when birds, bees, bats, butterflies, moths, beetles, other animals, water, or the wind carries pollen from flower to flower or it is moved within flowers. The successful transfer of pollen in and between flowers of the same plant species leads to fertilization, successful seed development, and fruit production. Other factors such as drought, extreme temperature shifts, or diseases may prevent full fruit and seed production. For more information, also see The Birds and the Bees.

Morphological Adaptation

Flowering plants have co-evolved with their pollinator partners over millions of years producing a fascinating and interesting diversity of floral strategies and pollinator adaptations. The great variety in color, form, and scent we see in flowers is a direct result of the intimate association of flowers with pollinators. The various flower traits associated with different pollinators are known as pollination syndromes. Flowering plants have evolved two pollination methods: 1) pollination without the involvement of organisms (abiotic), and 2) pollination mediated by animals (biotic). About 80% of all plant pollination is by animals. The remaining 20% of abiotically pollinated species is 98% by wind and 2% by water.

Wind

Plants that use wind for cross-pollination generally have flowers that appear early in the spring, before or as the plant's leaves are emerging. This prevents the leaves from interfering with the dispersal of the pollen from the anthers and provides for the reception of the pollen on the stigmas of the flowers.

In species like oaks, birch, or cottonwood, male flowers are arranged in long pendant catkins or long upright inflorescences in which the flowers are small, green, and grouped together, and produce very large amounts of pollen. Pollen of wind-pollinated plants is lightweight, smooth, and small.

Grasslands ensure successful wind pollination through sheer number of flowering plants and the large quantities of pollen released. Photo by U.S. Forest Service. Inset photo: A grass plant (Bouteloua gracilis) in anthesis (anthers releasing pollen). Photo by Steve Olson.

Some plants such as Erythronium grandiflorum stagger the timing of pollen release to increase visitation by pollinators and lower the chances of self-pollination. (Photo by Teresa Prendusi, US Forest Service.)

Wind-pollinated species like this cottonwood releases copious amounts of pollen from its catkins before the tree leafs out. Photo by Teresa Prendusi.

Clouds of pollen rise above an Engelmann spruce forest. Photo by Al Schneider.

Plants that are wind pollinated generally occur as large populations so that the female flowers have a better chance of receiving pollen. For more information, see Wind and Water Pollination.

Water

The small percentages of plants that are pollinated by water are aquatic plants. These plants release their seeds directly into the water. For more information, see Wind and Water Pollination.

Animals

Flowering plants and their animal pollinators have co-evolved where the forces of natural selection on each has resulted in morphological adaptations that have increased their dependency on one another. Plants have evolved many intricate methods for attracting pollinators. These methods include visual cues, scent, food, mimicry, and entrapment.