section_path: Pollination/Mechanisms/Self-pollination
section_name: Self-pollination
paragraph_text: Self-pollination
  
  Self-pollination is the pollination of the carpel of a flower by pollen from either the same flower or another flower on the same plant, leading to the creation of a genetic clone through asexual reproduction. This increases the reliability of producing seeds, the rate at which they can be produced, and lowers the amount energy needed. But, most importantly, it limits genetic variation. In addition, self-pollination causes inbreeding depression, due largely to the expression of recessive deleterious mutations.
  
  The extreme case of self-fertilization, when the ovule is fertilized by pollen from the same flower or plant, occurs in flowers that always self-fertilize, such as many dandelions. Some flowers are self-pollinated and have flowers that never open or are self-pollinated before the flowers open; these flowers are called cleistogamous; many species in the genus Viola exhibit this, for example.
  
  Conversely, many species of plants have ways of preventing self-pollination and hence, self-fertilization. Unisexual male and female flowers on the same plant may not appear or mature at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-incompatible. In Clianthus puniceus, self-pollination is used strategically as an "insurance policy". When a pollinator, in this case a bird, visits C. puniceus, it rubs off the stigmatic covering and allows for pollen from the bird to enter the stigma. If no pollinators visit, however, then the stigmatic covering falls off naturally to allow for the flower's own anthers to pollinate the flower through self-pollination.