Surprise Violets

Prairie Violet Photo Credit: Fontenelle Nature Association

An (admittedly blurry) prairie violet (Viola pedatifida) blooms on Oct. 9, 2017 in Knox County, Nebraska.

I ask a lot of questions when I walk through prairies and the Nebraska weather this year contributed to that process. The weather in 2017 was a yoyo. An unusually wet spring led to a hot, dry summer. The weather favored cool-season grasses, which do most of their growing in May and June and stunted warm-season grasses that do most of their growing in July and August. With little rain and intense heat, many plants in our prairies went dormant sooner than usual. Then we were treated to a warm, wet fall and we started to see some fun, weird things start flowering, like violets. Violets are usually one of the first flowers to bloom in spring. Prairie violet generally finishes blooming by late May or early June and then is finished for the year. But in 2017, we were seeing prairie violets break dormancy and bloom again in October, like the one below that I photographed on Oct. 9 in Knox County.

Violets are the required food for caterpillars of regal fritillary butterflies, which have been steadily disappearing from our continent in step with the loss of North America’s violet-rich tallgrass and mixed grass prairies. An estimated 1-4% of our tallgrass prairie remains. Nebraska contains some of the US’s most intact prairie, making our state an important harbor for regal fritillary butterflies.

But our regal fritillary caterpillars are not hatching in October so they were not feeding on the violets that bloomed in October, nor were there many insects at all to pollinate the violets. A little digging into violet biology taught me that while regal fritillaries need prairie violets, prairie violets do not necessarily need pollinators to produce seeds. In addition to the purple flower that is pollinated, a second type of flower with no petals can be found on the plant at ground level. Those ground-level flowers self-fertilize to produce seeds and appear to exist precisely because violets bloom so early in the spring that there may not be many pollinators around. With a second bloom in the fall, maybe we received a second dose of violet seeds to grow next spring, despite the lack of pollinators.

A regal fritillary butterfly drinks nectar on a red clover in June. Regal fritillary caterpillars feed on violets. Photo credit: Kelly Corman, NPLT

An interesting challenge for an unusual violet bloom in the fall is that the violets will be at a height disadvantage compared to when they bloom in the spring. In the spring, plants are just beginning to grow, so short plants like prairie violets have a chance to compete for sunlight. But in the fall, the 3-6 in. tall violets were blooming in the shade of taller grasses and other tall plants like asters that had had a full growing season to top the violets in height. Which made me ask: could the fall break in dormancy potentially stress the violet plants by using up valuable energy stores to bloom at a time when the shaded plants cannot access sun to store enough energy for next year?  Violets grow from a rhizome root system, so it is unlikely that a single season would affect their long-term energy stores, but what if fall blooms become more common in a changing climate?

Timing is everything. I wonder how climate change may affect regal fritillaries and their host violets. As our climate shifts and the timing of rain and temperature swings change, will the timing of caterpillar hatch and violet bloom change in the same ways in response? Or will they begin to mismatch? What does this mean for our prairie butterflies?

Author: Jen Corman, Coordinating Wildlife Biologist, Northern Prairies Land Trust