Self-pollination
Most of the self-pollinating plants have small, relatively inconspicuous flowers that shed pollen directly onto the stigma, sometimes even before the bud opens.
Self-pollinated plants expend less energy in the production of pollinator attractants and can grow in areas where the kinds of insects or other animals that might visit them are absent or very scarce—as in the Arctic or at high elevations.
Cross-pollination is the transfer of pollen, by wind or animals such as insects and birds, from the anther to the stigma of flowers on separate plants.
Self-pollination can lead to inbreeding depression caused by expression of deleterious recessive mutations,[2] or to the reduced health of the species, due to the breeding of related specimens.
In this system a single plant produces both open, potentially out-crossed and closed, obligately self-pollinated cleistogamous flowers.
Self-pollination in the slipper orchid Paphiopedilum parishii occurs when the anther changes from a solid to a liquid state and directly contacts the stigma surface without the aid of any pollinating agent.
[6] The tree-living orchid Holcoglossum amesianum has a type of self-pollination mechanism in which the bisexual flower turns its anther against gravity through 360° in order to insert pollen into its own stigma cavity—without the aid of any pollinating agent or medium.
This type of self-pollination appears to be an adaptation to the windless, drought conditions that are present when flowering occurs, at a time when insects are scarce.
[7] Without pollinators for outcrossing, the necessity of ensuring reproductive success appears to outweigh potential adverse effects of inbreeding.
[9] The lateral flow of the film of pollen along the style appears to be due solely to the spreading properties of the oily emulsion and not to gravity.
This raises the question of how meiosis in self-pollinating plants is adaptively maintained over extended periods (i.e. for roughly a million years or more, as in the case of A. thaliana)[13] in preference to a less complicated and less costly asexual ameiotic process for producing progeny.
An adaptive benefit of meiosis that may explain its long-term maintenance in self-pollinating plants is efficient recombinational repair of DNA damage.
