Beyond the bloom: Passion flower promotes ecological relationship

Do you have a passion for passion flowers? So do butterflies!

The passion flower vine is more than just a pleasant sight on a summer walk—it's also a host plant for butterflies. Here in Georgia, you will see butterfly pollinators such as the gulf fritillary, variegated fritillary and zebra longwing feeding off this plant. (A host plant is a species that serves as food for butterfly larvae.)



But interestingly, many species of passion flower plants have an adaptation that helps deter female butterflies from laying eggs on its leaves. Called "egg mimic," the plant's leaves have small dots on them that look like butterfly eggs.

The spots mean fewer caterpillars will be competing for the plant's leaves once they hatch. By escaping the caterpillars' voracious appetites, plants with these markings will have higher rates of survival and reproduction, so more of the population will have this inherited trait. And, studies have shown that female butterflies will avoid laying eggs on a plant that is already occupied in order to prevent competition.

But the purple passion flower that's native to Georgia (Passiflora incarnata) has a different kind of evolutionary strategy. It has extrafloral nectaries at the base of its leaves, which are button-like glands that produce nectar like a flower, but are not located in the flower. This allows the plant to make nectar all the time—not just when the plant is flowering.

This is important because ants are attracted to these nectaries, and will defend them—in turn, reducing damage that might be done to the leaves by other insects. So, while it's a different strategy than egg mimic, the end result is similar: reducing damage to the plant's leaves and increasing its chances of survival.

The next time you are out wandering, keep an eye out for this unique vine—you might just find some spiky gulf fritillary caterpillars on its leaves and tendrils, competing with the plant's own "bodyguards."