Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. Especially well known in peanuts, peas, and beans, this behavior is most widespread in the grass family. However, the largest genus of cleistogamous plants is actually Viola.
The more common opposite of cleistogamy, or "closed marriage," is called chasmogamy, or "open marriage." Virtually all plants that produce cleistogamous flowers also produce chasmogamous ones.  The principal advantage of cleistogamy is that it requires less plant resources to produce seeds than does chasmogamy because development of petals, nectar and large amounts of pollen are not required. This efficiency makes cleistogamy particularly useful for seed production on unfavorable sites or adverse conditions. Impatiens capensis, for example, has been observed to produce only cleistogamous flowers after being severely damaged by grazing and to maintain populations on unfavorable sites with only cleistogamous flowers. The obvious disadvantage of cleistogamy is that self-fertilization occurs, which may suppress the creation of genetically superior plants.
For genetically modified (GM) rapeseed, researchers hoping to minimise the admixture of GM and non-GM crops are attempting to use cleistogamy to prevent gene flow. However, preliminary results from Co-Extra, a current project within the EU research program, show that although cleistogamy reduces gene flow, it is not at the moment a consistently reliable tool for biocontainment; due to a certain instability of the cleistogamous trait, some flowers may open and release genetically modified pollen.
- Meeuse, Bastiaan and Sean Morris. 1984. The sex life of flowers. New York, NY: Facts on File Publishers. pp 110-111.