A Definition and Overview
The term “cultivar” is often a confusing topic among gardeners and non-gardeners alike. This problem is further compounded by differences of opinion as to whether cultivars can be considered native species and whether they should be planted in place of straight native species. This topic presents some intriguing questions for the home gardener.
“Cultivar” is a contracted version of two words—cultivated variety—which pretty well sums up its most basic meaning. Cultivars are plants which humans have selected and/or bred in order to retain some specific traits that appeal to us, such as unusual flower color, distinctively different shape or disease resistance. Cultivars are named by the grower or distributor following a standardized format. The plant retains its scientific name, genus and
Original Native Plant
Yarrow
Achillea millefolium
species (printed in italics), to which is added the new cultivar name, always surrounded by single quotation marks (never double quotation marks). For example, a cultivar of the redbud tree is Cercis canadensis ‘Forest Pansy’.
Cultivars are created by humans in one of three basic ways. The simplest and oldest method is to come across an individual plant growing on its own which naturally exhibits some unusual appearance or other desirable behavior. The second method is hybridization, where two different species or varieties of plants interbreed. Sometimes this interbreeding occurs naturally in nature when two related species bloom at the same time and cross pollinate. More often, however, humans purposely intervene and interbreed two species to create new traits. The last method is genetic engineering where humans directly manipulate the DNA of plants in the laboratory to get a specific trait. Cultivars of native plants almost always come from the first two methods. The third method is mainly used in medical, industrial and agricultural applications.
Once the desired plant trait has been identified, the next problem is how to make sure all future progeny of this plant have the same identical traits. There are two ways that these traits can be maintained. Plants can be grown from seed or they can be cloned which means they are grown vegetatively from the parent plant using techniques such as cuttings, tissue culture, and grafting. Although some native cultivars will grow true from seed, almost three-quarters of all native cultivars must be grown vegetatively in order to retain the desired traits.
Traditionally a cultivar is considered a version of a plant that is not genetically different enough to be considered a separate species. Thus it retains its scientific genus and species names. However, given the degree of human intervention, it is easy to see why people begin to question whether cultivars of native species are still natives. A native plant species is defined as one that occurs naturally in a particular region or ecosystem and was present prior to European settlement. In some instances, depending on the source of the cultivar, the plant may have been present prior to European settlement, but in most cases it very likely was not.
In an attempt to stress the fact that these plants are produced from native species and to draw attention to the exciting new cultivars of native plants appearing in the horticultural marketplace, Dr. Allan Armitage, Professor Emeritus from the University of Georgia, coined a new term “nativar” to describe cultivars of native species. It is a term that is getting increased recognition in the trade. As Sue Sweeney in her discussion of “The Nativar Dilemma” puts it, “’Nativar is a handy term becoming popular to describe ‘near natives’ of various sorts. The term covers any plant that is somewhat closely related to a local native plant but not quite it.”
For the home gardener, this growing abundance of cultivars of native plants presents a challenging range of choices. If a cultivar has been bred which has just the features that you want in your garden, then purchasing that particular plant makes sense. For example, you love the feathery green texture of the Bald Cypress tree but cannot possibly fit a 75-100 foot tall tree on your property, the dwarf cultivar ‘Peve Minaret’, which tops out at about 20 feet, might be just what you need. You can sort through various cultivars seeking the traits that meet your landscaping needs.
However, if you are growing native plants in your landscape as a means of providing food for wildlife or as a means of helping protect the native flora of your region, then the choices get a bit more tricky. As Vincent Vizachero points out in his article, “Native Culivars – Good, Bad and Ugly,” cultivars do not look like “normal or “typical” examples of a plant species. They behave differently and it is not clear if they perform the same ecological roles as the straight native species. There have been verified instances where the changes in a cultivar included unintended outcomes, such as insects and birds no longer recognizing the plant as a food source. Vizachero suggests that one can continue to plant cultivars as long as the flower shape, berry size and leaf color does not differ radically from the species and to never buy a cultivar touted for its resistance to insect damage. As a safety precaution, you can also keep an eye out to verify that birds, butterflies and other insects are continuing to use the plant as food. If not, it may be time to rip it out and replace the plant with something else.
Annie White, a PhD student at the University of Vermont has been conducting field studies to compare true native plants (open-pollinated) to native cultivars (human-bred) in terms of their ability to attract and support native pollinators. She studied 14 native species and 14 cultivars of the same species. She found that native species generally attract more pollinators and that the more similar the cultivar is to the species in flower shape and color, the more successful it is in attracting pollinators. In some plant species such as Purple Coneflowers, there was no or very little difference.
If protection and promotion of your region’s native flora is an important reason that drives your efforts to landscape with native plants, then you may want to consider the stance taken by the Wild Ones, an organization dedicated to preserving biodiversity through landscaping with native plants. The Wild Ones discourages use of cultivars. Cultivars are clones that are not cross pollinating in natural populations to produce their offspring, which means less genetic diversity and hence less adaptable plants. When using cultivars, you may be getting plant characteristics that you do not know and that may not be functional or ecologically effective. Even a cultivar that was originally found growing in the wild was only truly native when it was in its original habitat and reproducing naturally through open pollination. Another potential danger is that the cultivar may interbreed with the local genotype, either weakening it or destroying and replacing it. On the other hand, there may be no ecological harm at all. We simply do not know. To truly understand how cultivars will function in the local environment would require years of research for each and every cultivar produced.
The safest strategy, and the one that provides the greatest protection to our native flora, is to grow only straight native plants. These plants have the greatest genetic diversity, and genetic diversity is the best insurance policy for a plant species’ survival. It is also the best insurance that the plant will provide food to wildlife and pollinators, having evolved its role over thousands of years.
References:
Conlon, Hugh. “Nativars — New Cultivars of Native Plants.” What Grows There. 20 January 2014.
http://www.whatgrowsthere.com
University of Maryland Extension. Master Gardener Program. “ Part 7: The Future. Native Plant Species and Cultivars.”
https://extension.umd.edu/mg/part-7-future
Tennessee Smart Yards Native Plants 