Chasmogamy is a botanical term describing a type of flower. A chasmogamous flower opens at maturity, exposing stamens and style to allow fertilization. The style receives pollen from another individual. Chasmogamous flowers also provide pollen to other plants.
This is the opposite of cleistogamy, in which a plant produces flowers that stay closed and fertilize themselves. A cleistogamous flower is usually smaller and requires less energy to produce. It is also structured to bring its reproductive organs into contact, making it more likely that fertilization will be successful. Fertilization in a chasmogamous flower depends on the receipt of appropriate pollen, and often fails. Chasmogamous flowers are structured to maximize the receipt of pollen; they are generally larger and showier with markings such as nectar guides to facilitate the entrance of pollinators such as insects. They produce nectar, the reward sought by pollinating organisms, and are sometimes scented to attract them. The petals of a chasmogamous flower can be attractive to pollinators; cleistogamous flowers often lack petals.
Chasmogamy is a mechanism that can increase fitness via the exchange of genes between individuals. Cleistogamy is favored is stressful conditions, however, when producing large, complex flowering structures is costly to a plant. Cleistogamous flowers also occur in the absence of pollinators.
Some species have mixed mating systems, producing both chasmogamous and cleistogamous flowers. The ratio of flower types is often influenced by environmental conditions.
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- Berg, H. and P. Redbo‐torstensson. (1998). Cleistogamy as a bet-hedging strategy in Oxalis acetosella, a perennial herb. Journal of Ecology 86(3), 491-500.
- Culley, T. M. (2002). Reproductive biology and delayed selfing in Viola pubescens (Violaceae), an understory herb with chasmogamous and cleistogamous flowers. International Journal of Plant Sciences 163(1), 113-22.
- Diaz, A. and M. R. Macnair. (1998). The effect of plant size on the expression of cleistogamy in Mimulus nasutus. Functional Ecology 12(1), 92-98.
- Chasmogamy. Glossary. Royal Botanic Gardens, Kew.
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