Climate Change and Common Violets

In many Missouri backyards, a carpet of small purple or white violets is a sure sign of spring. In future springs, we’re likely to see more of these cheerful flowers earlier in the season as a result of climate change, a recent study from Garden researchers found. This may seem like an unexpected positive outcome of climate change, which threatens many of the world’s plants with extinction, but there’s more to the story, said Matthew Austin, a postdoctoral fellow with the Living Earth Collaborative at Washington University in St. Louis.

Viola sororia

The common blue violet, Viola sororia,is native to Eastern North America, including Missouri. This wildflower blooms in early spring, sometimes into late summer, producing blue-violet flowers or white blooms with purple veining. The genus name comes from the Latin name for sweet-scented flower. Its blooms attract butterflies. It is mainly pollinated by bees.

Violets reproduce both sexually, through cross pollination of the showy flowers we’re familiar with, and asexually, by self seeding of less noticeable flowers that remain hidden near the base of the plant. This is called “mixed mating.” Although environmental factors drive how much a plant reproduces sexually or asexually, no study had previously looked at the impact of climate change on mixed mating.

140 Years of Data

Austin, along with Garden Scientist Adam Smith, Piper Cole of New College of Florida, and Kenneth M. Olsen from Washington University, set out to answer this question using blue violets as a case study.

The team studied 131 blue violet specimens from the Garden’s herbarium from 1875 to 2015 paired with temperature and precipitation data to see if flowering correlated with climate. This is one of many potential scientific uses for the Garden’s expansive herbarium, which is one of the largest in the world with more than 7 million dried plant specimens.

“The specimens in the Missouri Botanical Garden Herbarium support a theoretically endless range of research questions, with new applications discovered and developed every year,” said Jordan Teisher, the Garden’s Herbarium Director. “The 131 collectors who ventured out into the Missouri landscape since 1875 could not have anticipated their carefully pressed and dried violets would be key contributors to a study of mating systems under climate change, but that is what makes biological collections so interesting and exciting – the unknown mysteries and untapped potential waiting to be discovered.”

The study found that violets produced fewer showy flowers in environments with warmer temperatures and less rain, while those in cooler climates with more precipitation produced more showy flowers. 

“It has been well documented that climate change is affecting the time of year that plants bloom,” Austin explained. “By finding that climate change is associated with increased production of sexual flowers, relative to asexual flowers, in the common blue violet, this study reveals that climate change might be affecting not just when plants reproduce, but how plants reproduce.”

Missed connections

As temperatures warm, violets are also blooming earlier in the year. More showy violets sooner in spring may seem like good news for those eagerly waiting for winter to melt away, but it could all be for naught if pollinators don’t emerge in time for earlier bloom times, Austin explained.

Climate change is causing many parts of nature to fall out of sync, which can be devastating for pollinators that emerge just at the right time to pollinate flowers they depend on. 

“These are often pollinators that only pollinate certain flowers or flowers that can only be pollinated by specific pollinators,” said Chris Hartley, Science Education Coordinator at the Sophia M. Sachs Butterfly House.

Additionally, the finding that wetter environments produced more showy, sexual flowers compared to asexual flowers could mean climate change is causing violets to produce more sexual flowers, or it could mean it is causing them to produce fewer asexual flowers. Producing fewer asexual flowers may be of concern, Austin said, because asexual flowers are key to violet reproduction when pollinators aren’t available to pollinate sexual flowers.

Next steps for this research will be to determine whether other species have responded to climate change in a similar manner as the common blue violet, and how changes to the production of sexual and asexual flowers have affected the genetic diversity of common blue violet populations, Austin explained.

“Genetic diversity is a key indicator of population health and is affected by whether plants reproduce by sexual or asexual reproduction,” Austin said. “By studying these phenomena, we can further our understanding of the ecological consequences of a changing climate.”

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