Pollination is the first step for all flowering plants during reproduction. When the transfer of pollen occurs between one plant’s anther and another plant’s stigma of the same species, it is called cross pollination. When the transfer occurs from the anther to the stigma of either the same or another flower borne on the same plant it is called self pollination.
Pollen grains travel via either biotic or abiotic vectors.
Biotic transference occurs when organisms are involved in moving the pollen grains. Examples of biotic vectors are insects, birds, bats, and other mammals. This type of pollination is responsible for over 80% of all pollination in flowering plants!
Remember, this means that they are also responsible for pollinating food crops! These biotic vectors are therefore responsible for creating the foods and raw commodities that go into processing and manufacturing the foods we eat.
You can find out all about biotic pollinators over here. We think pollinators are so important that they got their own page! Read up about why we think pollinators are awesome, learn about the issues they face, and what we can do to increase their numbers in the Metro Atlanta area through GAPP!
Abiotic pollination refers to the movement of pollen grain without the involvement of organisms. The most common examples of these vectors are wind (anemophily) and water (hydrophily).
The pollination rate of success for wind-pollinated species relies heavily on the plants’ surrounding habitat. Therefore, successful wind pollination is usually seen in things such as grasses and sedges, which usually grow in wide, open areas where pollen can be carried long distances easily and without obstruction.
However, imagine a different environment such as a rain forest. Thick, dense canopies would cause the obstruction of pollen flow, high amounts of water vapor would reduce the amount of pollen in the air, and high levels of plant diversity would decrease the probability of successful cross-pollination.
Considering the above scenario, wind pollination can seem very inaccurate and inefficient compared to its fellow systems of biotic vector delivery. However, there have been some adaptations by wind-pollinated species to increase the likelihood of success.
One of these adaptations that most wind-pollinated species share is that they produce high volumes of pollen. Even more importantly, this volume is much larger than the corresponding number of ovules which the pollen is targeting, leading to a higher probability of pollination and subsequent fertilization.
Secondly, the flowers of some wind-pollinated plants have large stigma present to “catch” the pollen grain. Some are described as being feathery or broom-like.
An interesting trait shared by most wind-pollinated species is that their flowers are often small, unobtrusive, lack nectar, and are not showy in color or shape. This is because they do not need to employ the “luring” techniques of those species which rely on attracting biotic vectors.
In wind-pollinated species, the flowers often lack the carolla and calyx, the most showy parts of the plants which attract abiotic vectors. With the carolla out of the way,
the stigmatic surfaces are more likely to be unobstructed, allowing for the pick up of pollen.
Some species of wind-pollinated plants have drooped structures called catkins which almost always have no petals. These structures develop predominantly as a male flower as in hazel or oaks, but can form both the male and female flower in species like poplar. Whether the catkins are developing as the male or female flower, or both, its easy to see why they would suit wind pollination.
The male pollen-producing catkins can hang down, away from the rest of the plant, and produce a large amount of unobstructed pollen for dispersal. As a female catkin, little to no petals will interfere with pollen drift and catkin droop (or erectness) would lead to an easier “catch”.