Pollinators preferred native Clarkia amoena over its cultivars.Jen Hayes/OSU
Planting native plants is a popular way to help support pollinators like bees, butterflies and other beneficial insects.
But when shopping for native plants, people often come across something called a "cultivar." This is a special version of a native plant that have been selected or bred to have certain traits, like different flower colors or shapes. These cultivated plants can look and behave a bit differently from the wild versions.
Researchers have been trying to figure out whether pollinators visit wild native plants more than they do cultivars, but past studies haven't been consistent in their results. According to Jen Hayes, a recent Oregon State University graduate, the findings were all over the map.
For her dissertation on native plants, their cultivars and pollinators, Hayes led a garden experiment at the OSU Oak Creek Center for Urban Horticulture in Corvallis that used a mix of wild native plants and their cultivated versions.
Over three years, Hayes and colleagues in the OSU Garden Ecology Lab(Link is external) watched and collected data on bees, butterflies and flower flies to see whether pollinators preferred one over the other, if certain pollinators favored certain types of plants, and if specialist pollinators -- those that rely on specific plants -- chose wild natives more often.
It was the first study of its kind to look closely at how pollinators like bees and butterflies interact with both wild native plants and their cultivated versions in the Pacific Northwest.
What they found was that pollinator visits depended a lot on the specific plant and insect. When comparing native plants with their cultivars, pollinators favored the wild versions about 37% of the time. Cultivars were preferred only about 8% of the time.
In more than half the cases, there was no clear difference.
"We found that visitation is dependent on the specific pollinator group and the plant group," Hayes said. "When we did see a difference in visitation rates, more often the native plant had a greater visitation rate than the cultivars. The cultivars that did have higher visitation rates tended to be those minimally developed cultivars."
Hayes cautioned that the results are based on a specific group of plants and a specific community of pollinators in one location, so that means results might vary in other regions, with different plants or under different environmental conditions.
Related:Asian long-horned beetle found in Michigan
For example, the researchers observed many specialist bees -- those that only visit certain types of flowers -- and especially one group that's common in the central Willamette Valley. That's not always the case in other studies, Hayes said.
A native cultivar is one that has been selected from a native population or a cross that's been developed by humans, said Signe Danler, online instructor for the OSU Extension Service Master Gardener program. Breeders select for characteristics that people are drawn to, such as larger and more abundant flowers, a variety of colors, longer bloom or more compact form.
The cultivars are distinct, uniform and stable, meaning they will remain the same with each generation. The best way to tell the difference is that a cultivar will have its name listed in single quotes after the scientific name as in Echinacea purpurea 'White Swan.'
"When we create cultivars, we create a version of a native as we like it," Danler said. "And since many are propagated clonally (from one cell) they never change. Genetic variability stops."
Cultivars aren't harmful
It's not harmful to grow cultivars in the garden, Danler said, but they should never be used in restoration projects, where genetic variability is key so plants can adapt. Cultivars of native plants are propagated to minimize genetic diversity in favor of uniformity.
Related:Slime time: Outsmart slugs to save crops
For the study, Hayes divided pollinators into categories: all pollinators, wild bees, bumble bees, leafcutter bees, longhorn bees, syrphid flies and butterflies to represent the diversity of the pollinator population at Oak Creek.
There were only two plant groups where pollinators seemed to consistently prefer the native plant, including Clarkia amoena or farewell-to-spring, and Eschscholzia californica or California poppy. The plant with the strongest storyline, however, was Clarkia, Hayes said. Pollinators in five groups preferred the species over the cultivar, which could be because the species blooms longer and, in more abundance, so pollinators have more time and flowers to visit.
There were some pollinator groups where yarrow (Achillea millefolium) and Douglas aster (Symphyotrichum subspicatum) cultivars were more visited by pollinators than the species. Yarrow by honeybees; Douglas aster by honeybees, bumble bees and the all-pollinator group.
"The cultivars we used represent a spectrum of plant breeding modifications," Hayes said. "Some just had a different flower color or a change in foliage like variegation. Others were more developed, like interspecific hybrids, which are plants resulting from parents of at least two different species. All the cultivars had a wild-type native plant somewhere in its pedigree."
Wide range of colors
People used to believe that pollinators stuck to specific flower colors -- bees to blue and yellow, butterflies to red and so on. But in this study, bees visited a wide range of flower colors, including pinks and purples. What really seems to matter is a mix of traits like nectar quality, bloom time, flower size and even how flowers are arranged on the plant, according to Hayes.
"Some groups are fervently anti-cultivar," Hayes said. "I don't think that's fair. I came into the study thinking that I preferred natives just because I had assumptions about the ecological benefits. There is intrinsic value to planting native plants in the landscape, but it's not fair to villainize cultivars."
Hayes said cultivars can be valuable, like in the case of American chestnut trees that were decimated by the chestnut blight in the early 1900s.
"There might not be American chestnut trees left in the country if breeders weren't working on developing resistant cultivars," Hayes said. "It was a way to potentially restore a keystone species. In some ways, cultivars can be ecologically important and should be used. Or if someone wants to have their favorite plant in every color or a special cultivar that means something to them, who am I to tell them not to?"
The study was funded by grants from the Native Plant Society of Oregon, the Garden Club of America and Sherry Sheng.