August 25, 2025August 22, 2025
In times of extreme temperatures — like Upstate South Carolina’s record-setting 42 consecutive days this summer with temperatures at or above 90 degrees — some flowers have a competitive edge.
Two studies by researchers at Clemson University showed that flowers with traits that help them thermoregulate have advantages over those that don’t when it comes to reproduction and ability to attract pollinators.
“We’ve known for a while that temperature impacts plants’ reproductive performance as well as photosynthetic rates and growth rates. Pollen viability and ovule viability can be reduced during extreme temperatures, so it should be advantageous to have mechanisms to deal with those conditions,” said Matthew Koski, assistant professor in the Department of Biological Sciences.
Koski said that in extreme temperatures, pollinators can show different preferences for floral temperature.
Instead of focusing on the consequences of floral temperature for reproduction and plant-pollinator interactions, a study published in the American Journal of Botany focused on identifying the traits that modify temperature, particularly cooling the flower during high heat.
Matt Koski, Clemson University College of Science.
Shape and color
Koski and Jennifer Apland, who graduated from Clemson with a master’s degree in ecology and evolutionary biology in 2023, studied how shape and color of flowers affected their temperatures.
They studied eight flowering plant species based on color and floral architecture in a subalpine meadow in southwestern Colorado. They compared flowers that were yellow and others that were blue, pink and purple.
For floral architecture, they selected two shapes — bowl-shaped like buttercups where the petals open up and the flower’s reproductive structures and nectar rewards were exposed to solar radiation and tubular like snap dragons where the petals form a tube, encapsulating the reproductive structures and nectar.
The researchers used tiny thermocouple probes to measure the temperature experienced by the reproductive structures of the flowers and placed additional thermocouple probes to measure air temperature.
“We were measuring temperatures at the exact time in the same habitat on different species,” Koski said.
Differences found
They found that flowers with exposed reproductive structures warmed more than those with concealed reproductive structures, and this effect was strongest for yellow flowers. Closed flowers were more thermally stable than open flowers regardless of color.
“The flowers that have these kind of enclosed microenvironments remain cooler under higher temperatures because they are shading the reproductive structures,” Koski said.
Traits can also affect the way pollinators see a plant when they are foraging, said Apland, who is now collections coordinator at the Michigan State University Herbarium.
“Foraging is like walking into the grocery store and you’ve got name brands that have these bright logos that draw your attention. But this bright branding might have other effects, too,” she said. “There are all of these complex interactions in creating traits and then how a pollinator, or this shopper, perceives them.”
Pollinators can behave differently based on their environments, she said.
For instance, when it’s really cold, pollinators will “sit” inside of a tubular flower to warm themselves up, almost like crawling into a sleeping bag during a cold camping trip and warming yourself up before you pack up and continue hiking, Apland said. Conversely, if it’s really hot outside, pollinators will stop foraging and instead fly around in circular patterns. It is thought that the air running past them as they fly helps them cool down, she said.
Tubular flowers such as the Skyrocket (Ipomopsis aggregata) remain cooler in higher temperatures.
Pollinator’s choice
The second study focused on whether the pollinators choice of a flower was based on the flower’s temperature, and if a flower’s temperature is influenced by the air temperature.
Apland created artificial flowers out of cardstock and paint to isolate floral temperature as much as possible.
“We didn’t want pollinators to select based on floral color, shape or size. We wanted to control that as much as so we could directly tie rates of visitation to floral temperature. One way we did that was to focus on reflection of near infrared light,” she said.
Near infrared is outside the visual spectra of bees so these wavelengths can generate a lot of heat that bees can’t see.
“For us, we can’t see UV light, but we know it exists. Same thing with bees, they can sense the warmth, but they can’t see this warmth,” she said. “So, we were able to affect this floral temperature without affecting what bees see.”
Change in foraging behavior
The way the pollinator groups foraged changed based on air temperature and the temperature inside the flower, Apland said.
When air temperature was high (86 degrees F), cooler flowers received more visits than warmer flowers. When temperatures were cool, pollinators — specifically fly pollinators — spent more time in warmer flowers. However, flies foraged longer in cooler flowers when air temperatures were warm. Flower temperature impacted the likelihood of bee basking but not their visitation rate or foraging duration. Visitation rates for bees depended on air temperatures. As air temperatures increased, the number of bee visits increased.
“By isolating floral temperature from other floral traits, we found direct effects of flower temperature on visitation and behavior of wild pollinators, especially during periods of more extreme air temperatures,” she said. “Pollinators have the potential to exert selection on floral temperature and the traits that shape it.”
Extreme temperatures affect plants in many ways
Apland said that one of the big takeaways is how extreme temperatures are affecting plants in so many different ways, like reducing the viability of pollen, the ability to set seed, and the number of pollinators that visit and spend time in the flower. “Plants that are able to regulate their temperature are seeing increased pollinator visitation, she said.”
Koski said another takeaway is that if we can look at the natural variation that occurs among flowers and find traits that help flowers cool off under extreme temperatures, selective breeding might be possible in economically important species.
Detailed findings on the floral shape and color study were published in the journal American Journal of Botany in an article titled, “Floral shape and color impact heat accumulation and thermal stability of the floral microenvironment in a subalpine meadow.”
The findings of the study on floral temperature and pollinator visits were published in the British Ecological Society journal “Functional Ecology in an article titled, “Isolating the effects of floral temperature on visitation and behavior of wild bee and fly pollinators.”
Want to Discuss?
Get in touch and we will connect you with the author or another expert.
Or email us at news@clemson.edu
Comments are closed.