Challenges with Cultivars

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Echinacea purpurea ‘Pink Double Delight’. When the native plant movement began in the 1970s, one of its goals was to educate the public about landscaping and gardening in an ecologically sustainable way. A half-century later, the buy-in has been more than anyone bargained for.
Photo by Corine Holtmaat

The growing number of native plant enthusiasts demanded innovations in native flora available at local nurseries. In response, the horticulture industry provided an increasing number of cultivated forms of native plants designed to enhance desirable traits, such as attractiveness to pollinators, aesthetic value, disease resistance, and consistent performance. Nursery growers and breeders in the United States and abroad, in both the native plant community and the ornamental sector, had cultivated these new plants from ones selected in the wild and hybrids created in laboratories. Unfortunately, both cultivated wild selections and hybrids were often lumped under one generic label: “native cultivar” or, simply, “cultivar.” Confusion ensued, controversy erupted about ecological value, and the topic boiled into one of the plant world’s hottest debates: Do cultivars provide the same benefits to wildlife as the species from which they’re derived, or are they just ornamentals with no environmental value? Even worse, could native plant cultivars cause environmental harm?

The horticulture community is divided on the answers, because opinions differ on taxonomy, botany, basic terminology, and more. Luckily, a home gardener doesn’t need to acquire a deep knowledge of plant genetics to find answers to questions about cultivars. All you have to do is decide the purpose of your garden.

Phlox paniculata ‘Jeana’ is a popular selected cultivar.
Courtesy of Mt. Cuba Center

For the Home Gardener

If you like the latest trends in ornamental breeding, then hybrid cultivars will likely appeal to you. Hybrids are propagated asexually by breeders who cross — and, in some cases, backcross — two or more species. Hybrid flowers can be sterile, especially double-flowered forms, but this isn’t the case with hybrids in general. Many Echinacea and Penstemon hybrids, for example, produce nectar, pollen, and seed. But there’s something else to be aware of with hybrids: Studies have shown that anthocyanins that turn green leaves purple or red to give them a visual pop add a bitter taste that discourages insect foraging.

If your aim is to support wildlife and the food web, then selected cultivars are for you. These are straight species plants chosen from natural populations because they possess desirable garden characteristics, such as mildew resistance or a smaller size than the typical species. The vast majority of selected cultivars are produced vegetatively from plant parts, and most of them retain the ecological benefits of their wild counterparts. Because these cultivars are genetic duplicates of the parent plant, they can never offer the genetic diversity that ecological restoration practitioners require to rebuild plant communities. This, however, doesn’t diminish their value in urban or suburban gardens.

Trillium grandiflorum ‘Pamela Copeland’ is a rare natural double flower 
Courtesy of Mt. Cuba Center

Echinacea purpurea is a readily available species.
Courtesy of Mt. Cuba Center
One example of a selected cultivar is Phlox paniculata ‘Jeana.’ It was discovered by Jeana Prewitt growing along the Harpeth River near her home in Nashville, Tennessee. Named for her, it was selected for propagation because its dark-green leaves resist powdery mildew, which is unusual for the genus. Plus, its sweetly scented flowers, which are smaller than the species and bloom in varying shades of vibrant lavender-pink from midsummer through early autumn, strongly attract pollinators.

“There are certain plants that have specific longstanding relationships with butterflies and bees,” says Steve Castorani, whose wholesale North Creek Nurseries in Landenberg, Pennsylvania, popularized ‘Jeana.’ “I can tell you 100 percent that if you put this plant in your yard and it blooms, you will have tiger swallowtail butterflies. It’s a one-to-one relationship.”

An additional validation of the ecological value of ‘Jeana’ is that it was identified as a star pollinator plant in the Phlox Sun Trials at Mt. Cuba Center, a nonprofit botanical garden in Hockessin, Delaware, that encourages a broader use of native plants to support wildlife and conducts field experiments of selected and hybrid cultivars to evaluate their garden-worthiness.

A member of Mt. Cuba Center’s Pollinator Watch Team collects pollinator data in the Trial Garden.
Courtesy of Mt. Cuba Center

Dealing with Double Flowers

Mt. Cuba Center recently completed a trial evaluating 75 different coneflowers (Echinacea), including some with double flowers that are examples of the hybrid cultivars widely available in the nursery trade. “As part of the trial, we’ve been evaluating 12 doubles and even dissected some of them, and found that none of the double-flower coneflowers in our current trial produce seeds,” says Jeff Downing, executive director of Mt. Cuba. “While it’s biologically plausible that some double-flower forms may produce pollen and nectar, it is uncommon.” 

Mt. Cuba is sourcing a double-flowered coneflower that’s popular with consumers for trial, Echinacea purpurea ‘Pink Double Delight’, to determine if it produces pollen and nectar. This plant was the first successful commercial introduction of double flowers, says Angela Treadwell-Palmer, founder and co-owner of Plants Nouveau in Mobile, Alabama. She’s also the breeder agent for AB-Cultivars in the Netherlands that developed the plant.

“We have never touted the doubles as food for wildlife or for genetic diversity, but simply as decorations for gardens, as many horticultural perennial introductions are,” Treadwell-Palmer says. “The pollinators do visit them, and, in my horticultural and ecological opinion, they are much better than turf. So I would rather see someone begin with a double coneflower because they thought it was pretty, fall in love with it, and then move on to collect others, even single-petaled selections with enhanced wildlife benefits.”

If you want to dig deeper into Mt. Cuba Center’s trials on Echinacea species and cultivars with pollinator data, you can view its 2018 to 2020 research report at Echinacea for the Mid-Atlantic Region.

A volunteer citizen scientist collects pollinator data in Mt. Cuba’s Trial Garden
Courtesy of Mt. Cuba Center

Plant Presence at Nurseries

Gardeners who prefer straight native species likely believe their only choice is to buy cultivated forms because that’s all they see in plant nurseries or catalogs. They can take comfort in knowing their eyes aren’t deceiving them. Mt. Cuba conducted and published a survey in April 2017, updated in February 2018, of 14 wholesale nurseries in Virginia, Maryland, New Jersey, and Pennsylvania. Of the 6,885 different plants sold by the target nurseries, only 25 percent were native. This percentage includes straight native species and selected and hybrid cultivars. Of the natives, just 23 percent were straight species, meaning 77 percent of native plants available to consumers were cultivated forms. The survey authors did note, however, that omitting box store growers in the survey was a flaw that could’ve changed the results.

Treadwell-Palmer adds another perspective about why hybrid cultivars dominate nursery benches. “A lot of times, a cultivar is chosen because it has more vigor, more flowers, or it just plain propagates or grows better. … Other times, a plant is selected because it looks really great in a 1- or 2-gallon pot on a retail shelf, and that attracts customers at retail,” she says. “The saddest reason plants are selected is because growers who are shipping plants to chain stores can fit more plants on a rack, so they choose the shortest selections for that reason. Many cultivars are shorter. Breeders are convinced Americans have no gardens or smaller gardens, so they make everything fit smaller spaces.”

Doug Tallamy (right) guides the capture and study of insects at Mt. Cuba Center.
Courtesy of Mt. Cuba Center

Altered Traits in Hybrid Cultivars

When buying hybrid cultivars, gardeners should be aware of traits in the species that have been altered, says Robert Wyatt, research professor emeritus at the University of North Carolina at Chapel Hill and former professor of botany and ecology at the University of Georgia. “Understanding which traits have been changed provides clues about the cultivar’s ability to perform the same ecological role as the species,” he says. Wyatt says the traits that are most frequently changed are stamens and pistils that have been converted into extra petals or bracts that provide no nectar, pollen, fruit, or seed to nourish wildlife; anthocyanins that have been introduced to turn normally green leaves purple or red but that reduce palatability to insects that feed on them and, sometimes, attractiveness to pollinators; larger or smaller plant size; changes in flower colors; altered plant growth; and earlier or later flowering times than the native or straight species.

It’s understandable, Wyatt believes, that the gardening public might not understand how some altered traits could make some hybrid cultivars poor candidates for supporting wildlife. “We’re still trying to make inroads with the largest part of the general public in terms of understanding why native plants are better for the landscape and garden than some nonnatives, and better than cultivars in many cases, though certainly not all,” he says. “One of the best things people can do to understand why native plants are so important is to read Doug Tallamy.” Tallamy is a professor in the department of entomology and wildlife ecology at the University of Delaware, and the inspirational leader of America’s native plant movement. Many native plant enthusiasts consider his work Bringing Nature Home the go-to book for understanding the critical link between native plants and native wildlife.

The Debate Continues

Wyatt, whose emphasis has been plant reproductive ecology, says he greatly admires the work Tallamy and others have done in entomology, but adds that the altered traits in cultivars that concern him most are ones involving changes to the flowers. “I am more concerned in some ways about plants that totally mess up reproductive systems by converting flower parts into more petals to make them more showy, or where they have changed flower color. That’s where a study Annie White did at the University of Vermont is so interesting.” White, then a student working toward a doctorate in ecological landscape design, evaluated 12 native herbaceous plant species and 14 native cultivars. She found that only one cultivar with different-colored flowers than the species attracted more pollinators than the species. Because of the proliferation of hybrid cultivars in the nursery trade and findings such as White’s, Wyatt is concerned that “cultivars that don’t fill the role in the food web that their ancestors have for millions of years could wreak havoc on natural ecosystems.” 

Not everyone agrees with this view, including Downing. “In a suburban pollinator garden, there are vanishingly few situations I can imagine where the genetic heritage of your coneflowers and Coreopsis are likely to threaten the vitality of a local ecosystem,” he says. That’s the point Mt. Cuba and the U.S. Botanic Garden were trying to make when they convened a panel of biologists, geneticists, restorationists, and statisticians in 2017 to begin to provide some rational guidance for individuals seeking to feed wildlife and promote healthy biodiversity by using native plants. They di­s­covered that what’s appropriate and necessary in a restoration project is different from what’s beneficial and advisable in a suburban garden.

Downing thinks it’s great that some home gardeners choose to garden with seed-grown straight species as opposed to asexually created cultivated forms of any kind. But he also agrees with the panel’s approval of a more nuanced approach to gardening. “If you’re a backyard gardener who just wants to use native plants to attract and feed bees and butterflies,” he says, “you can head down to your local garden center with a little knowledge of how plants grow; pick up some cultivated Tiarella, Monarda, and Asters; add color to your garden throughout the seasons; and feel at ease that you haven’t just wrecked nature.”

‘Nativars’: A New Name for Native Plant Cultivars

The term “nativar,” which refers to cultivars of native plants, seems to have snuck its way into the horticultural lexicon. No one really knows when or how it came into use—not even the person who coined the term, Allan Armitage, professor emeritus of horticulture at the University of Georgia. “It’s at least five years old, maybe more,” Armitage says. “I write books and articles. Maybe I just stuck it in there somewhere. All of a sudden, people were asking me, “Why did you write nativar?’ Well, it seemed to make sense to me.”

Armitage thinks using the term “cultivar” to refer to cultivated forms of native plants confuses people. “What is a cultivar?” he asks. “It’s just a cultivated variety. It could be anything. What’s a nativar? Well, it’s a variety of a North American native plant. When you say ‘nativar,’ people immediately know you are talking about a native plant.”

For the record, he says, the term refers to both propagated selections of native plants as well as lab-created hybrids. “Whether a cultivar occurred naturally or somebody created it in the lab or greenhouse, it’s still a hybrid, and it’s still a cultivar,” he says. “In fact, I would guess that 95 percent of what is offered today are hybrids.”

Armitage’s belief is that gardening should be simple. If gardening sounds too complicated, he says, people’s eyes will glaze over and they’ll lose interest in what should be a fun, relaxing, and enjoyable hobby. He thinks keeping that levity is especially important during the coronavirus pandemic. With people staying closer to home, indications are that many are turning to gardening, perhaps for the first time.

In the meantime, Armitage is just grateful that some people listened and recognized that “nativar” came from him. “Not that I’m going to make any money from it,” he says. But it’s nice to know I left something for the world.”

Because his lectures have been canceled due to the pandemic, Armitage is inviting people to walk through his garden with him on Facebook Live. Join him at Armitage Allan.

Tom Oder is an independent journalist living in Atlanta, Georgia, who writes about gardening, the environment, and agribusiness.

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