- By Susan Martin
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July 2020-Vol.6 No.7
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- 28 Comments
There is a lot of excitement about planting native plants, and the reasons for choosing them are well-researched. However, when home gardeners look for native plants in nurseries, they often find cultivars of natives rather than straight species. Straight species native plants have grown in a particular area or ecoregion for hundreds or even thousands of years, are open-pollinated, and grow true to seed. Many plants marketed as “natives” in garden centers have never grown naturally in the wild. The word cultivar means a cultivated variety; to meet the definition of a cultivar, a plant must be bred asexually. Some cultivars originated as “sports” or mutations that were discovered in the wild. Most cultivars, however, are the result of selective breeding by humans. Hybrids are the result of a genetic cross between two different species. A plant label will give the genera and species in italics, followed by another descriptive name in single quotes. This last name indicates that the plant is a cultivar. An example of a naturally occurring cultivar is the eastern redbud tree, Cercis canandensis ‘Appalachian Red’. This native, fuchsia-pink- to red-flowered tree was discovered growing along a road in Maryland. The purple coneflower cultivar, Echinacia purpurea ‘Pink Double Delight’, is a hybrid developed by plant breeders for its showy double blooms.
Cultivars are developed for attractive characteristics such as striking flower colors; shorter, bushier forms; colored or variegated leaves; winter hardiness; and improved disease resistance. These qualities make them easier to incorporate into a home garden design, particularly when space is limited. There have been many field trials on native cultivars that assess these “improvements” relative to the straight species and to different cultivars. Gardeners can look up the findings on specific plants to see which cultivars have performed best. This article, however, focuses on a different aspect: “Do native cultivars provide the same benefits to our home garden ecosystems as straight species native plants?”
To answer this question, we’ll focus on current research. At this point, there are two main areas of study. The first looks at woody plants, and the effects of cultivar characteristics on leaf-eating insects, caterpillars in particular. The second area focuses on herbaceous plants, and the effects of cultivar characteristics on pollinators.
Readers who would like to refresh their familiarity with terms such as straight species, open pollination, variety, cultivar, and hybrid, can refer to a past article from The Garden Shed on plant nomenclature.
WOODY NATIVE CULTIVARS AND NATIVE LEAF-EATING INSECTS
Many of us are familiar with Douglas W. Tallamy, noted entomologist from the University of Delaware and author of Bringing Nature Home (2007) and Nature’s Best Hope (2019). Although his research has been ongoing for many years, he more recently has been conducting research trials at the Mt. Cuba Center with doctoral student Emily Baisden. The studies focus on whether cultivars of native woody plants are as productive as straight species, productive in the sense of supporting native insects, caterpillars in particular. Gardening for wildlife, such as butterflies, birds, and bees, requires plants that can support juvenile stages of insects, not just the nectar-sipping adults.
The field study included 16 species of woody plants, both trees and shrubs, with cultivars of each species, for a total of 160 plants. The species were planted in the middle of a ring surrounded by the cultivars matched to each species. Tallamy chose cultivars that varied from their straight species counterparts in one of four ways:
- plant habit
- disease-resistance
- leaf color variation
- increased berry size
His team studied three insect behaviors: how lepidoptera caterpillars react to the changed characteristics found in cultivars; how and whether hatching bagworms recognize plant differences; and the overall insect impact on the plant during a season. Researching insect response takes years to reach conclusions. To appreciate the challenges of setting up a trial study and collecting data, as well as a listing of plants in the study, and a discussion of study results, see this video of Kim Eierman of EcoBeneficial interviewing Tallamy. Or, read a transcript of Eierman interviewing Tallamy.
Ninebark (Physocarpus opulifolius) Photo: courtesy of U.S. Fish & Wildlife Service
Ninebark ‘Autumn Wine’ (Physocarpus opulifolius) Photo: Susan Martin
Do his study results vote yay or nay on using cultivars? The only trait out of the four that consistently deterred insect eating was changing green leaves to red or purple or blue.
As Tallamy explains, “Red leaves remove chlorophyll from the leaf and load it with anthocyanins, which just happen to be feeding deterrents.”
Regarding the other cultivar traits, slight variegation did not affect insect feeding; however, as the percentage of variegation increased, the leaves became less attractive. Changing plant habit, such as making a shrub more compact, had no effect on insect feeding. On the other hand, the larger-berried highbush blueberry cultivars supported more insect species than their straight species counterparts.
As Tallamy has noted, “What we’re looking at is different types of genetic changes, and then we can extrapolate because there’s no way we’re going to look at all tens of thousands of cultivars. Fortunately, there are only a few types of genetic changes that create a cultivar. We are looking for patterns that emerge from these few changes.”
Cultivar research offers opportunities for important work on plant diseases. Preliminary results of Tallamy’s study of American elm (Ulmus americana) indicate that the ‘Princeton’ cultivar, which is resistant to Dutch elm disease, is no less attractive to insects. A very good sign, according to Tallamy who holds great hope for the introduction of “back-crossed” American chestnuts (Castanea dentata) that were almost eradicated in the last century by chestnut blight.
HERBACEOUS NATIVE CULTIVARS AND POLLINATORS
The next area of research to cover is the comparison of native plants vs. cultivars of natives with regards to pollinators. Several studies have conducted comparative field trials, the first undertaken by Dr. Annie White of the University of Vermont (2016) in replicated research gardens at two sites in northern Vermont (see photo of Maidstone Plant Farm at top of article). The field trial included 500 plants, 14 native species with native cultivar pairings. For a description of the study, a listing of species and their pairings, and study results for particular plants, see White’s blog (3/01/16), From Nursery to Nature: Are native cultivars as valuable to pollinators as native species? You may also wish to see a video of Kim Eierman’s interview with White on her study and results.
Asclepias tuberosa. Photo: Sarah Bingham
Asclepias tuberosa ‘Hello Yellow’. Photo courtesy of Missouri Botanical Garden PlantFinder,PlantFinder/Mo.Botanical Garden
What her studies have revealed is that the more manipulated the cultivars became, the less attractive they became to pollinators. Therefore, if considering native cultivars for use in a pollinator garden, open pollinated seed-grown “selections” or “sports” (naturally occurring mutations) are the best choices. Cultivars that differ significantly in color and morphology from the native species should be used cautiously. (Morphology is a study of the form of things. In plants, it includes the roots, stems, leaves, flowers, and fruits.) White hypothesized that color differences and decreased nectar and pollen production in hybridized cultivars are the leading factors. However, she also cautioned that cultivars should be evaluated individually. White found that about half of the cultivars in her study were comparable to the native species, and about half were inferior. It’s important to note that although the cultivars in the study were sometimes less attractive to pollinators than the native species, the cultivars were still visited by pollinators. This suggests that cultivars provide valuable floral resources in the landscape. For example, all pollinators combined exhibited a significant preference for Agastache foeniculum over the cultivar Agastache ‘Golden Jubilee’. However, ‘Golden Jubilee’ had a higher mean pollinator visitation rate than all but two other native species in the study. There were also cases when the native cultivar was equally attractive, such as Aesclepias tuberosa and the cultivar Aesclepias tubersosa ‘Hello Yellow’, a naturally occurring mutation in the natural population. One native cultivar selection, Veronicastrum virginicum ‘Lavendelturm’ (Lavender Towers) attracted significantly more total pollinators than the native species and had a longer bloom time.
Tallamy’s research showed that making a woody plant more compact did not change its attractiveness to leaf-feeding insects.But White found that compact form for herbaceous plants does seem to have an influence on pollinator attraction, because compactness often equates with fewer flowers per plant and fewer floral resources.
A comparison of the straight species, Echinacea purpurea and three Echinacea cultivars focused on altered traits of color, compactness, double-flowered, hybridization, and sterility.
Echinacea purpurea Photo: Sarah Bingham
Echinacea purpurea ‘White Swan’ Photo: Susan Martin
Echinacea purpurea ‘Pink Double Delight’
Photo courtesy of Missouri Botanical Garden PlantFinder,PlantFinder, Mo. Botanical Garden
Results of the study showed pollinator preference for the straight species, E. purpurea, followed by E. purpurea ‘White Swan’, an open-pollinated seed cultivar of E. purpurea. The interspecific hybrid, Echinacea ‘Sunrise’, a cross between two different species of Echinacea, was less attractive to pollinators. The double-flowered cultivar, E. purpurea ‘Double Pink Surprise’, was the least attractive. The reproductive organs (stamens and carpels) in double-flowered varieties have been modified into additional petals, thus rendering the plant sterile or near sterile, and reducing the quantity and/or accessibility of floral rewards. These results are consistent with the recommendation to use open-pollinated cultivars that are true to seed. Choosing a cultivar that’s as close to the native species as possible—in morphology, bloom time, and color—is going to increase the likelihood that it’s a comparable substitution.
NECTAR REWARDS
White also studied patterns of nectar production in two native species of Lobelia, L. cardinalis and L. syphilatica, and four native cultivars. One cultivar had nectar equivalent to the species, but the rest of the cultivars had less. One cultivar had only 20% of the nectar available from the species. This means that when pollinators are attracted to the cultivars, they may have to work harder to get energy rewards equivalent to their visits to native species. White is studying not just the quantity of nectar produced by flowers but also the quality. In this video, using Monarda fistulosa, she shows how she measures both the standing nectar, which is the amount of nectar at any time, and the secretion rate, which is how quickly the plant can reproduce nectar. With sugar content ranging from about 15-75%, not all flowers are equally valuable to pollinators. She will study the differences in nectar production between native species and cultivars, and she plans to measure pollen in future research as well.
ADDITIONAL RESEARCH ON POLLINATOR ATTRACTION
Phlox paniculata ‘Jeana’ Photo: Missouri Botanical Garden Plantfinder,PlantFinder, Mo. Botanical Garden,
Phlox paniculata. Photo courtesy of Missouri Botanical Garden Plantfinder,PlantFinder, Mo. Botanical Garden
At the University of Delaware, Keith Nevison, a graduate student (2016) with Dr. Deborah Delaney, conducted field trials at Mt. Cuba. He compared insect attraction, nectar quality, and floral characteristics between U.S. Eastern Phlox species and associated cultivars. In total, 6 straight species, and 10 cultivars were evaluated for factors having the greatest influence on insect visitation. Results suggest that certain Phlox cultivars, especially those selected from the wild, are more attractive to insects than their straight species counterparts. Cultivars Phlox ‘Jeana’ and ‘Lavelle’ were far more attractive to pollinators than the straight species Phlox paniculata. This is presumed to be due to the ease with which the insects were able to get at the nectar in the narrow-shaped flowers. Both cultivars also had high nectar volume and sucrose content, making them ecologically beneficial to feeding pollinators. For the majority of Phlox cultivars, however, insect attraction and nectar quality did not differ significantly in comparison to their associated straight species. In the case of Phlox paniculata and its cultivars, the narrowness of a flower’s corolla, in particular, has a strong influence on insect attraction. Like White, Nevison cautions that native cultivars need to be considered on a case-by-case basis. In addition, more experimentation in different parts of the country over a longer time frame may yield different results.
Also at the University of Delaware, Deborah Delaney and graduate student, Owen Cass, are looking at how well various plants attract insects by assessing floral traits such as color, nectar and pollen quantities, and the nutritional qualities of nectar and pollen. They are comparing differences among cultivars within two genera: Coreopsis and Monarda. Plans are to use the diverse selection of flowers present at Mt. Cuba Center to develop a pollen library for commercial and hobbyist beekeepers. Study results have not yet been published.
OTHER WILDLIFE CONSIDERATIONS
It is important to note that although the larger fruits produced by some cultivars, such as the highbush blueberry, may be more attractive to insects, larger berry size may be problematic for some birds. In addition, although more compact form on woody plant cultivars did not deter insect feeding, a more compact form might negatively affect bird nesting. This reminds us to consider ways in which cultivar characteristics might impact wildlife in addition to insects.
BIODIVERSITY AND NATIVE CULTIVARS
A major consideration when using human-bred and hybridized native cultivars in the landscape is the loss of genetic variation naturally found in open-pollinated plant populations. Humans reproduce most hybrid varieties through vegetative propagation, either by tissue culture, or by cuttings and divisions, making hybrids genetic clones of each other. This sameness can make our planted landscapes more vulnerable to disease, pests, or other disruptions.
There is also the potential for cultivars to hybridize with surrounding populations of native species. According to the Maryland Cooperative Extension, studies have shown that, in some cases, cross-pollination with cultivated varieties resulted in the loss of the wild species. This loss has ramifications for all the species that interact with the native plant. Or, cross-pollination with strong cultivars can make wild species stronger. Although this could benefit the plant species, increased vigor could also make the wild relatives more effective at competing with other plant species, putting the balance of the ecosystem at risk.
Sterile cultivars of native plants can’t cross-pollinate with their wild relatives, so they pose no risk to wild plant populations. Sterility is a two-edged sword, however, because sterile cultivars may have reduced pollen and nectar production. As White points out:
Breeding for sterility can inhibit flowers from setting seed, hence resulting in longer bloom duration. This could be a benefit to pollinators if the flowers continue producing ample nectar and pollen, but this is often not the case. Degrees of sterility can vary among cultivars, along with quality of nectar and pollen production, making it important that floral resources for pollinators are evaluated on a plant-by-plant basis. To our knowledge, nectar and pollen production have not been studied in Echinacea cultivars, but in other species, male-sterile cultivars have significantly decreased nectar and pollen flow.
Additionally, gardeners need to consider the impact of sterile, non-seed-producing cultivars on seed-eating bird populations.
COLLABORATIVE RESEARCH
In 2017, a diverse group including representatives such as ecologists, geneticists, public garden professionals, government organizations, and research/cultivar developmental entities, met to discuss the development of an analytical tool that would evaluate which native species and/or native cultivars might be appropriate to different planting objectives and to different planting sites. Sites were identified as: 1) large, undisturbed sites identified as candidates for restoration, that were in proximity to wild plant populations or, 2) small, highly disturbed sites that were isolated from wild plant populations, such as urban gardens. For the large undisturbed areas, native species were recommended as essential for restoration. For the small sites, the group proposed a lower risk/higher rewards trade-off analysis for including cultivars that met various criteria. For information on their recommendations, see this report.
A CALL TO HOME GARDENERS
Four botanic gardens (Chicago Botanic Garden, Denver Botanic Gardens, North Carolina Botanic Garden, and San Diego Botanic Garden) are asking home gardeners to join a study across the country to investigate whether cultivars of native plants or “nativars” (a popular term, rather than a scientific term, often used in casual reference or in marketing) provide the same pollinator service as native species. Since spring 2018, participating public gardens have been planting popular native species with matched cultivar pairings to compare pollinator use. In addition, home gardeners are being asked to watch such comparisons in their own gardens, and to complete weekly 10 minute observations while flowers are blooming, and record the number and type of pollinators that visit. Data will be uploaded via the Budburst Data Portal. The Nativars Research Project runs through fall 2022. For information on the native plants and native cultivars recommended by geographic area, pollinator identification, guidelines on how to participate, and to register with Budburst, go to this link.
SUMMARY
At first, we were so happy to have a “simple” way to help the environment: plant native plants. But then the cultivars started multiplying, and the choices became more difficult. Were we even asking the right questions? Fortunately, there is good research, and more is coming. Studies have shown that cultivars aren’t always good, and they’re not always bad. In fact, goodness and badness can be partly defined by our gardening priorities. Researchers have concluded that cultivars of native plants should be evaluated on a case-by-case basis. The research is providing us with a framework for analysis: does the native cultivar exhibit characteristics similar to the species plant, or has the cultivar been altered too far from its origin? Annie White advises, “Choosing a cultivar that’s as close to the native species as possible—in morphology, bloom time, and color—is going to increase the likelihood that it’s a comparable substitution.” This means, of course, that we must begin by knowing the species’ characteristics, and how they’ve been altered in the cultivar.
SOURCES
“A Gardener’s Guide to Plant Nomenclature, II,” The Garden Shed, https://piedmontmastergardeners.org/article/a-gardeners-guide-to-plant-nomenclature-part-ii/
“Are Native Cultivars Ecologically Beneficial? Interview With Dr. Doug Tallamy,” Kim Eierman EcoBeneficial.com, https://www.ecobeneficial.com/audio/are-native-cultivars-ecologically-beneficial-an-interview-with-dr-doug-tallamy/
“The Nativar Conundrum: New Research on Natives vs. Native Cultivars with Dr. Doug Tallamy,” Kim Eierman, EcoBeneficial.com, https://www.ecobeneficial.com/2015/10/the-nativar-conundrum-new-research-on-natives-vs-native-cultivars-with-dr-doug-tallamy/
Bringing Nature Home, Douglas Tallamy, Timber Press, 2007
“From Nursery to Nature: Evaluating Native Herbaceous Flowering Plants Versus Native Cultivars for Pollinator Habitat Restoration,” Annie White, University of Vermont ScholarWorks @ UVM, Graduate College Dissertation and Theses (2016), scholarworks.uvm.edu › cgi › viewcontent
“From Nursery to Nature: Are native cultivars as valuable to pollinators as native species?” pollinatorgardens.org., https://pollinatorgardens.org/2013/02/08/my-research/
“Native Cultivars vs. Native Plants & Their Attractiveness to Pollinators,” Kim Eierman, EcoBeneficial.org, https://www.ecobeneficial.com/2014/04/native-cultivars-vs-native-plants
“Native Cultivars vs. Native Plants with Annie White,” Kim Eierman, EoBeneficial.org, https://www.ecobeneficial.com/videos/native-cultivars-vs-native-plants-annie-white/
“Nectar Collection and Analysis,” Kim Eierman, EcoBeneficial.com, https://www.ecobeneficial.com/videos/nectar-collection-analysis/
“Cultivars of Native Plants,” University of Maryland Cooperative Extension, https://extension.umd.edu/hgic/topics/cultivars-native-plants
“Nativars Research Program,” Chicago Botanic Garden, Budburst Project, https://budburst.org/projects/nativars
“Considering a Role for Native Plant Cultivars in Ecological Landscaping: an Experiment Evaluating Insect Preferences and Nectar Forage Values of Phlox Species vs. its Cultivars,” Masters Thesis, Keith A. Nevison (2016), University of Delaware, http://udspace.udel.edu/handle/19716/21442
“The Role of Native Cultivars in the Ecological Landscape: Evaluating Insect Preferences and Nectar Quality in Phlox and Its Cultivars,” Keith Nevison, Ecological Landscaping.org., https://www.ecolandscaping.org/01/designing-ecological-landscapes/native-plants/the-role-of-native-cultivars-in-the-ecological-landscape-evaluating-insect-preferences-and-nectar-quality-in-phlox-and-its-cultivars/
“Nativars (Native Cultivars): What We Know and Recommend,” Habitat Network (A Partnership Between The Nature Conservancy and the Cornell Lab), https://content.yardmap.org/learn/nativars-native-cultivars/
“Flower Power: Cultivars vs. Straight Species,” The Humane Gardener, https://www.humanegardener.com/flower-power-a-qa-with-annie-white/
“What’s in a Nativar?” Landscape Architecture Magazine, Carol Becker, https://landscapearchitecturemagazine.org/2019/07/02/whats-in-a-nativar/
“Sourcing Native Plants to Support Ecosystem Function in Different Planting Contexts,” Restoration Ecology, https://onlinelibrary.wiley.com/doi/full/10.1111/rec.12931
“Native Plant Partnership,” UDaily, University of Delaware, http://www1.udel.edu/udaily/2015/jul/healthyecosystems070714.html
Feature Photo of Plant Trial Gardens, Maidstone Plant Farm, University of Vermont, Dr. Annie White.
marjie giuliano I just read your article and found it extremely informative and wonderfully educational. I am a PMG but certainly not one of the best informed. As a member of the VNPS, this topic has worried me for a long time and has been a source of frustration with friends who strive to collect the “special” cultivars, while I always encourage the natives. Though I have not had all the knowledge to make a convincing argument, you have presented great examples and encouragement. Thanks so much for this clear, inclusive, and lovely article on this topic which seems to have had far too little emphasis. I would welcome you enthusiastically as a speaker to any of the VNPS meetings after just seeing this article referenced in the PRISM newsletter. What a nice way to start a dreary day… thanks so much!
Susan Martin Thank you so much for your comments. It is an important topic, and one which many of us run into when we’re trying to find straight species natives. It takes the work of understanding the characteristics of the species before you can understand how the cultivars may affect caterpillars and pollinators. Many times, it’s difficult to find the straight species. After reading more about nativars, I’m not tempted any more on the basis of ornamental value. I am trying to learn more about Doug Tallamy’s position on looking at natives for their “productive” value, how they provide food for caterpillars. He advises us to be “fussy” about the plants we pick and make sure they’re adding value to the ecosystem. Productive natives” is such an interesting concept and if we want to make a difference with one yard at a time, we should be thinking about how to pick the most productive native plants.
Lynn Roberts I just read your article. It was very informative, even for someone with little experience in this area. It is somewhat disheartening though. It is difficult to find native plants, especially non-toxic ones that will be safe around my animals… and now I find out there’s another level of trickiness involved. : ) I am glad I found your article before purchasing anything, still in the collecting ideas phase.
Susan Martin I’m assuming that you’re concerned about pets, such as dogs and cats, or is it farm animals? Our dog eats everything and likes berries, so I planted a serviceberry tree out of her area because the berries are listed as poisonous to dogs. I’m not worried about leaf toxicity, because I’ve never seen her eat foliage, other than grass. But you’re right, it is something to be aware of. I have also learned “too late” about some plants that are less than optimal. I bought a ninebark cultivar (Physocarpus opulifolius) with reddish leaves before I realized that changing green leaves to reddish or purplish wasn’t a good thing to do as far as caterpillars are concerned. I recently turned down a cultivar of sweetshrub (Calycanthus floridus) because the primary changed characteristic seemed to be large flowers, which is not characteristic of the species. I didn’t know how that would affect pollinators. Instead of being disheartened, I try to think of it as moving up the learning curve and learning how to do things better. Unfortunately, I seem to be moving a little slower up that curve than I’d like! But it’s gratifying to figure out how I can improve things. You may also want to look at the article, A Year of New-Home Landscaping and What I’ve Learned. You sound like a curious person who wants to do things as “right” as you can. Thanks so much for commenting.
Sue Madison I am so thankful to whomever posted this article. I have been a proponent of natives for some time without considering the “cultivar” vs “wild” native issues. Now I am better educated and have more to consider. I am relieved I don’t have any cultivars with unusual leaf colorings.
Susan Martin There’s a lot to learn and more research is being conducted that will help us evaluate the benefits of straight species natives vs. cultivars of natives. We’ll keep you posted! It’s a fascinating and important area of research.
Nancy Whitehead I’m planting one border of a new (very small) park at our local library. I wanted to do all natives, but have been captivated by some cultivars – ‘Lemony Lace’ for our elderberry (Pacific NW), ‘4ever Goldy’ for western red cedar, choosing these based on their ultimate size and our ability to maintain them. I got exactly the information I’d been looking for in your article and a link, and I thank you very much.
Susan Martin The pros and cons of using cultivars of native plants need to be evaluated when it comes to selecting plants that are easy to maintain, work within the overall landscape plan, and suit site conditions. This is especially true when working on a public site such as a library. Being familiar with the research on native plants, native cultivars, and pollinator benefits will help you make those decisions. Thanks for taking the time to comment.
Susan Martin Thanks for your comment. The Garden Shed staff will be sure to revisit this important topic and report on new research.
Patrick Turgeon Great article! This is an well-structured and easy-to-understand summary of this very important topic. I appreciate the work that went into creating this piece.
Susan Martin Thanks so much for taking the time to comment. It helps us identify topics that are important to our readers. We’ll revisit this topic as new research becomes available.
Tammy Taylor Finally! I have searched extensively on this particular topic and have found little information. We started gardening a few years ago and want to bring pollinators into our garden. This got me thinking about the current sterile flowers I have around my house and garden. Are they good for and do they nourish the bees, butterflies and hummingbirds? My gut feeling was, probably not, but I could not find much information. I am redoing my flower garden this spring and will not be adding sterile plants. Thank you so much for your research into this important matter!
Susan Martin Thanks so much for your comment and for raising an interesting point about applying the research on a practical basis. According to research by Annie White as reported in the article: “Degrees of sterility can vary among cultivars, along with quality of nectar and pollen production, making it important that floral resources for pollinators are evaluated on a plant-by-plant basis. To our knowledge, nectar and pollen production have not been studied in Echinacea cultivars, but in other species, male-sterile cultivars have significantly decreased nectar and pollen flow.” The research reported in this article did not conclude that all hybrids are sterile. However, if you choose not to plant any hybrid cultivars so that you can avoid plants that may not optimize pollinator benefits, that’s certainly an option. The Plant VA Natives campaign is labeling straight species natives as well as some native plant cultivars with red tags at participating nurseries. Pollinator benefits of native cultivars is a really interesting area of research, and we’ll report on updated info.
saasa I just read your article. It was very informative.
Very good summary.Susan Martin Thanks so much for taking the time to comment. We appreciate your input.
Doug Call me a purest, but given the availability of straight native species from so many places like prairiemoon.com for example, I don’t see the need for using cultivars.
boca88 Very good post. I just wanted to mention that I really like your post. I hope you continue to provide useful posts like this.
Susan Martin Thank you for taking the time to comment. There is so much ongoing research on this topic, and we appreciate hearing about your interest in being updated.
Tom Thank you. Really good info and appreciate the clear sourcing and transparency.
Susan Martin Thanks so much for commenting. This is an important topic that will need updating.
Heather M I apologize for the dumb question, but are cultivars and hybrids the same thing? When I look at a tag on a hybrid plant, it always has a name in single quotes like cultivars do. An example I’m thinking of is a Nellie Stevens holly. It’s a cross between Ilex aquifolium and Ilex cornuta, and it’s propagated asexually. Oh my goodness, I’m SO confused.
Susan Martin Perhaps the easiest way to address your question is to look at Echinacea, or purple cone flower. (See this Garden Shed article for more background info.) But first, let’s look at the definitions of cultivar and of hybrid. I would also refer you to this past Garden Shed nomenclature article which gives a detailed explanation of species, variety, cultivar, and hybrid.
A cultivar is a plant or grouping of plants selected for desirable characteristics that can be maintained by propagation. Most cultivars have arisen in cultivation, but a few are special selections from the wild. Most cultivars do not produce true-to-type seeds, meaning plants must be reproduced vegetatively through cuttings, grafting, and tissue culture.
In horticulture, a hybrid is defined as the offspring of two plants of different varieties, species, or genera. Deliberate hybrids or accidental hybrids in cultivation are considered cultivars.
Now for the echinacea example. It’s generally agreed that there are 9 different species of echinacea, although some reports differ on this exact number. There are over 200 cultivars. A cultivar means cultivated variety. Although there can be naturally occurring mutations in the wild, most cultivars are purposefully selected for specific, desirable characteristics and then bred for those characteristics. The first breakthrough echinacea cultivar was E. purpurea ‘Magnus.’ This cultivar, introduced in 1998, has rosy-purple petals that spread out flat rather than drooping like most coneflowers. Another big echinacea cultivar breakthrough was the double-flowered coneflower. In 1997, Jan van Winsen of The Netherlands found a double-flowered seedling in his cut flower fields. It was the first of its kind in the world. It was eventually successfully marketed as E. purpurea ‘Razzmatazz’ in 2003. So, at that point there were E. purpurea cultivars with flatter heads that didn’t droop as much, a brighter color, and some with double flowers. At the Chicago Botanic Garden, Jim Ault was working on breeding different species of coneflowers to produce colors other than pink. He produced the first orange coneflower, which was called Echinacea ‘Art’s Pride,” introduced in 2004. He did this by crossing two different echinacea species, E. purpurea ‘Alba’ and E. paradoxa (yellow coneflower). Cross-pollinating by hand, it took Ault 6 years and more than 200 plants to get this introduction. ItSaul Plants in Atlanta was also developing Echinacea cultivars at about the same time.
To address your question on plant labeling, although a hybrid plant is identified with an x in its name, the labeling is often shortened in the trade and may just appear as a cultivar. I would again refer you to this article on nomenclature.Peggy Singlemann Susan,
I enjoyed reading your article and I thank you for summarizing the research on nativars. Fortunately, Mt. Cuba Center’s research starts to answer the questions about the cultivars of some species of plants. I hope you and my fellow readers enjoy this report on Echinacea found at:.
https://issuu.com/mtcuba/docs/20033-echinacea_report-interactive?fr=sNTE0YTI0NjAxNDg
Also on Mt. Cuba Center’s website is a list of the research results on other native plants trialed over the years. I found while reading each plant evaluation within a study is where I learned about the pollinator values of the trialed cultivars and varieties. https://mtcubacenter.org/research/trial-garden/.
Happy Gardening!
Peggy SinglemannSusan Martin Peggy, thank you so much for reminding our readers about these very valuable resources. I have always so enjoyed your presentations and TV show on gardening! Congratulations on your recent retirement from Maymont Foundation. I would just quickly summarize for our readers that the Mt. Cuba trial on Echinacea evaluated pollinator attractiveness as well as the horticultural appeal of 75 different echinacea species and cultivars. The straight species, E. purpurea, which is probably the species most common to most of our readers, ranked second in pollinator attractiveness with an average of 83 daily visits. The top rated was an E.purpurea white cultivar, ‘Fragrant Angel’ which had 85 visits. So the straight species did very well! The study pointed out that straight species echinacea tend to favor poorer, drier soils than the soils of the Mt. Cuba trial gardens. This difference may have affected the species’ horticultural ratings. The trial also confirmed that double-headed cultivars have less pollinator appeal than single headed flowers. The second source you cited from Mt. Cuba reports on the plant trials that have been completed so that you can check on a particular species. Thanks so much Peggy for pointing out ongoing research!
Laura Sheppeard Thanks so much for this detailed article. So many gardeners are adopting the view that aliens and cultivars can’t support local wildlife. Your article shows this isn’t necessarily true, and that choosing what to plant, and what to keep, is much more complicated. It is especially concerning that home gardeners, and some government programs, are using pesticides to kill aliens or cultivars, regardless of their wildlife value. And ripping out healthy trees, shrubs, and ornamental grasses whose roots are sequestering carbon. We can choose better plants as space allows, and replace truly undesirable plants when they fail or become too much of a problem.
Susan Martin Thanks so much for taking the time to comment. I wanted to point out that when evaluating the benefits of nonnative plants, we all need to be familiar with nonnative plants that are invasive. I’m sure you’re aware of this, I just needed to make this distinction for readers. For example, crepe myrtles are not native to North America, but they are not considered invasive, and they do provide pollen and nectar, particularly pollen, for bees at the end of the summer when other floral sources are less abundant. There are interesting studies at the University of Georgia on the preferences of different bee species, including native bees, for different crepe myrtle cultivars. If I were choosing a new tree to plant, I’d choose a native species but I personally wouldn’t remove an exiting crepe myrtle because it has benefits. It also does well in full sun, while many of our native flowering trees prefer some shade protection. On the other hand, the invasive tree, Ailanthus, or Tree of Heaven, is extremely invasive and acts as a host for the Spotted Lanternfly. This insect from China attacks grapes, fruit trees, and other trees. It also supplants native plants. It can only be eradicated with the use of herbicides, but this tree needs to be eradicated despite the disturbance. Other invasive species such as autumn olive, oriental bittersweet, and stilt grass, take over the forest under story and need to be eradicated. Some of these invasive plants are abundant in our own home landscapes and we need to get rid of these before they spread. So, you’re right in pointing out that there is a more complicated evaluation when deciding what to replace with native plants, but the evaluation of whether a species is invasive needs to head the list.
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