Pollination Takes Two (or More)

When it comes to pollination, plants consist of those that don’t require pollination (like ferns), plants that use the wind for pollination (like oaks, pines, and grasses), and plants that need insects to do the job. It is the case of insect pollination that I want to highlight here.

Over many years, plants and insects have evolved together for the mutually beneficial act of pollination. We all know what plants get out of it: they make more fertile seed with pollination and the cross-pollination between plants means that they are genetically more diverse (which is good for species survival). Insects benefit too: some of them go for the protein-rich pollen as a food source while others want the nectar. Some do both.

Flowers evolved to have bright petals to attract insects. In some cases, certain insects became specialists on certain flowers. For those that collect pollen, visits from flower to flower take a bit of pollen from one flower and, in the process of collecting more, transfer it to the next when the insect goes to the other flowers of the same type. For insects that collect nectar, the flower has evolved to ensure that the collection of nectar doesn’t shortchange the plant’s need for pollination, sometimes depositing pollen on the insect so that is has to carry it to the next one. I call these situations ‘accidental pollination.’

Bumble bee and Centrosema virginianum, stamens exposed
as the bee goes for the nectar

Bee exits with pollen on its back to exchange with next flower

Regardless of how it happens, cross-pollination is more effective when large numbers of flowers are present. I was reminded of this increased effectiveness this week as my spurred butterfly peas (Centrosema virginianum) started flowering. Although I had two plants growing together, few flowers appeared the first week (and perhaps only on one of the plants, it was hard to tell) and none of them produced seed pods.

The next week, flowers were everywhere – easily 10 of them at once! Bumble bees were visiting them constantly. I was excited to capture how they went after the nectar, pushing up the spur to get to the nectar and, in the process, exposing the stamens and stigma to an exchange of pollen on the back of the bee itself. As a result, many of the flowers have resulted in seed pods.

Seed pod forming on Centrosema virginianum

So for better pollination as well as improved genetic diversity, keep in mind that it might take two to get the best result. Plant accordingly.