Ruellia strepens

24 February 2019

The benefits of cleistogamous reproduction

"Perfect" flowers have both male and female parts--ovule-bearing pistils and pollen-bearing stamens. This means that they could potentially pollinate themselves, but may plants go to great lengths to avoid this. Some plants will avoid self-pollination by protandry (male parts mature first) or protogyny (female parts mature first). Other plants deem their own pollen as incompatible and can short circuit self-pollination. Still other dioecious plants, such as hollies, have entirely separate male and female plants so an individual could never self-pollinate.

Then there are plants that don't care to follow any of these rules. Ruellia strepens, pictured above, often relies on self-pollination for reproduction. Its perfect flowers never even open to entertain the idea of cross-pollination. Scientists call these flowers "cleistogamous," which translates as "closed marriage." The Violas are another genus that often employ cleistogamy. It takes energy and resources to attract pollinators to boost cross pollination--some plants produce showy inflorescences, others provide nutrient-rich nectar and pollen. Cleistogamy eschews cross-pollination and produces seeds that are veritable clones. In small populations, this may be a better strategy than risking low seed set and inbreeding depression through traditional cross-pollination.

Scientists have much to learn about how and why plants conduct reproduction. We do know that pollination strategies can change because of genetics, population size (how do plants know how many other plants are nearby?!), available resources and pollinator presence. This is an exciting field of study that will no doubt bring us more information in the coming years.

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