Final answer:
Spring ephemerals often have cleistogamous flowers because they enable the plants to reproduce after the forest trees leaf out, which reduces light availability and may limit pollinator activity. Cleistogamy is a self-pollination strategy crucial for the survival of these plants in changing light conditions and pollination dynamics due to climate change.
Step-by-step explanation:
Spring ephemerals like the spring beauty (Claytonia virginica) often have cleistogamous flowers as an adaptation to their environment. These flowers allow for self-pollination without opening and often occur after the plant has already produced typically open, cross-pollinated flowers. This strategy is beneficial because once the trees in the canopy leaf out completely in late spring, the light availability decreases significantly. Cleistogamy ensures that these plants can still reproduce successfully even with the limited light and potential lack of pollinators.
Cleistogamy can be seen as an adaptation to the specific timing of ephemerals' life cycles, which must be completed before the canopy trees absorb most of the sunlight. In addition, with the effects of climate change, flowering times and the presence of pollinators may not always align, making cleistogamous flowers an important fallback strategy for reproductive success.