What environmental conditions favor cleistogamous flowers?

Cleistogamous flowers are favored under environmental stress or unstable conditions where cross-pollination chances are low. They evolve as a survival strategy to ensure self-fertilization and seed production even when external pollinators or resources are limited.

Environmental Conditions Favoring Cleistogamy

1. Low Light or Shaded Conditions
   Plants growing under low light conditions or dense canopy environments often develop cleistogamous flowers because energy resources are insufficient to produce large, open, and nectar-producing chasmogamous flowers.
2. Drought and Low Moisture
   Cleistogamous flowering is promoted in dry, water-limited environments where conserving energy and water is crucial. For example, Viola sororia shows increased selfing through cleistogamy during drought and high-temperature conditions.
3. Low Pollinator Availability
   In ecosystems with limited insect activity or fluctuating pollinator populations (especially in colder or high-altitude areas), plants favor cleistogamous reproduction to ensure seed set without reliance on external agents.
4. Cool or Unfavorable Temperatures
   Cleistogamous flowers prevail in cold or variable climates, such as temperate forests, where pollinator activity is reduced, and the risk of cross-pollination failure increases.
5. Seasonal and Resource Stress
   During late or unfavorable seasons (autumn or winter), plants like Lamium amplexicaule produce more cleistogamous flowers as part of an adaptive plastic response to seasonal shifts and competition for limited nutrients.
6. High Environmental Variability
   Regions with unpredictable fluctuations in temperature and precipitation—such as tropical dry forests, deserts, and mangroves—often select for cleistogamous species as a “bet-hedging” mechanism for reproductive assurance.

In essence, cleistogamy is favored in low-resource, low-pollinator, and highly variable environments where self-fertilization is a reliable fallback mechanism to secure reproductive success.