Cleistogamy

Cleistogamy is a reproductive strategy in flowering plants in which flowers never open, and self-pollination occurs within the closed floral organs. This mode provides seed production when pollinators are scarce or environmental conditions are unfavorable for open flowering.

There are two main patterns. Obligate cleistogamy describes plants that produce only closed flowers and self-fertilize without outcrossing. Facultative cleistogamy refers to species that generate both cleistogamous (closed) and chasmogamous (open) flowers; the latter allows occasional outcrossing when conditions let pollinators visit open flowers.

Mechanistically, cleistogamous flowers are typically small and inconspicuous, with reduced petals. Pollen sheds inside the bud and reaches the stigma while the flower remains closed, so fertilization occurs without floral opening. Seeds from cleistogamous flowers are usually genetically homogeneous, reflecting selfing, and are often produced with minimal resource expenditure.

Ecological and evolutionary implications include reproductive assurance in the absence or unreliability of pollinators, and potential reductions in genetic diversity and adaptive potential due to selfing. Cleistogamy is common in many herbaceous plants and is especially well-documented in grasses; many species can produce both types of flowers, providing a flexible mating system that responds to environmental conditions.