native [ NAY-tiv ] adjective, noun: originating, living, or growing naturally in a particular region or ecosystem; a species indigenous to a place or habitat
non-native or alien [ EY-lee-uhn, EYL-yuhn ] adjective, noun: (of a species) “with respect to a particular ecosystem, an organism, including its seeds, eggs, spores, or other biological material capable of propagating that species, that occurs outside of its natural range”1
invasive [ in-VAYS-siv, in-VEY-siv ] adjective: (of a species) “with regard to a particular ecosystem, a non-native organism whose introduction causes or is likely to cause economic or environmental harm, or harm to human, animal, or plant health”1
Native plants are those that occur naturally in a given region and ecosystem, which over the course of time have adapted to the physical conditions of those locations in co-evolution with other species in that system. Some species may be endemic within a fairly large area, but make further adaptations to very specific local growing conditions within that range. For example, red maple trees exist over a wide range of climate zones in the United States, but the red maples that thrive in Florida may not survive in a New Hampshire winter; conversely, the maples that thrive in New Hampshire may not survive a southern summer. The two locations require what some botanists call different local provenance or ecotype, and this kind of specialized localization has led some to a narrower definition of what “native” means in the plant world. Further complicating the nuances of what species are considered native in a given ecosystem is climate change, which is changing the places where some plants can thrive, and will likely continue to do so. As climate warms, plants may move further north, or to higher altitudes, or begin to die out, factors that then affect the fauna that have co-evolved to depend on them. For optimal ecological impact in native plantings, scientists recommend that gardeners source their plants from the same ecoregions they will plant in, using the appropriate ecotypes so the local fauna will be those to whom these plants are familiar.
Clematis virginiana (pictured above left and center, in a residential landscape in Arlington, Virginia) can spread rapidly but as a Virginia native is not considered an invasive species unlike alien Clematis terniflora, native to Japan, China, and Korea, which often escapes cultivation and overtakes native vegetation (pictured above right, growing rampantly on public lands near the Mount Vernon Trail north of Alexandria, Virginia).
Although some native plants can be aggressive, perhaps spreading more rapidly than gardeners would like and outcompeting other species that might be preferred, that aggressiveness is different from being invasive, a word applied to non-native plants (also called aliens or exotic aliens) that create havoc when introduced into new environments from other places. Non-native plants are less useful than natives, which often provide specific insects with pollen and/or nectar, or serve as a leafy food source for the larvae (caterpillars) of butterflies and moths or otherwise serve local fauna. Some define non-native plants as those that have arrived on this continent in the centuries since European colonization began. As new settlers arrived, they often brought with them plants and animals that were familiar to them as food sources or even just beloved and familiar ornamentals in their home countries. Over the centuries and through new waves of immigration, more people from a wider range of places have likewise imported plants as food or forage. Longtime resident populations have also imported non-native plants for particular purposes, such as erosion control, higher productivity, better drought tolerance, or simply led by the desire to possess beautiful and rare or exotic species. Or, they have taken favorite plants, indigenous to their particular state or region, and moved them elsewhere within the US where they do not naturally grow. Additionally, sometimes new species arrived inadvertently as fellow travelers in clothing or luggage or uninvited passengers on motor vehicles or in the holds of ships or planes.The tendency to want something from one’s place of origin or as a tool for a particular purpose can, however, have unintended consequences.
Kudzu planted as forage on a Georgia farm in the 1950s and smothering flora as it spreads unrestrained in Atlanta, Georgia in 2006.
An egregious example of good intentions gone wrong is the kudzu vine (Pueraria montana), which is a bane on the landscape throughout the southeastern US, and still spreading. Kudzu is native to Japan and southeast China, and was first imported for the Philadelphia Centennial Exposition in 1876. It was touted as a “great ornamental plant” for its sweet-smelling flowers and sturdy vines. From the mid-1930s through the 1950s, the US Department of Agriculture’s Soil Conservation Service (now National Resources Conservation Service), formed in response to the depredations of the dust bowl era, recommended kudzu as a useful way to control erosion, and it was planted along roads and around fields. Farmers found it grew quickly and produced up to two crops of nutritious livestock fodder that they baled up as a form of hay, until the vines got too big and heavy, reducing the nutrient value of the leafy crop. Kudzu grows about a foot a day and spreads via runners and rhizomes as well as seeds, killing competing vegetation by growing over and covering it, shading out all sun, and preventing photosynthesis. As climate change warms the earth, the plant is spreading further and further north and west. Attempts to control and eradicate come at great economic cost, including the cost of crops lost to these exotic aliens.
Left to right: Invasives spreading on fences and overhead power lines (Ampelopsis brevipedunculata and Wisteria), smothering trees and other flora (Celastrus orbiculatus, Hedera helix, and Lonicera japonica), invading shore and woods (Rosa multiflora and Vinca minor), and for sale in nursery pots (Berberis thunbergii)).
Some invasives spread via berries or seeds eaten by small mammals and birds. Examples of harmful invasives that kill their native competitors by aggressive spread, out-shading with vigorous growth, strangling with strong vines, using up available water and nutrients, and similar tactics, include Ampelopsis brevipedunculata (porcelain-berry), Berberis spp. (non-native barberries), Celastrus orbiculatus (oriental bittersweet), Clematis terniflora (Japanese clematis), Hedera helix (English ivy), Lonicera spp. (non-native honeysuckles), Rosa multiflora (multiflora rose), and Wisteria spp. (Chinese and Japanese wisterias). Vinca minor (periwinkle), sold as an attractive ground cover, can invade a whole garden by being used as a spiller plant in a single pot of geraniums on a front porch if it reaches down even one of its graceful spiller branches and puts down a foot in the flower bed next to the steps, where it roots and then races to spread its runners. So many of these plants were imported or adopted for what gardeners or landscapers or governments of the time thought were good reasons: hardiness, beauty, lovely scent, color, tolerance for poor soil, drought, etc. The doctrine of unintended consequences was too often forgotten. Today’s horticulturists must bear this in mind as they cope with climate change, invasive insects or other challenges lest the intended cure be worse than the current problem.
Despite the havoc caused by invasive plants, many nurseries continue to sell them, so gardeners need to be aware of what species are considered invasive in their particular area. State and local governments usually have this information available online (see the lists for Virginia, City of Alexandria, and Arlington County). The best way to control invasive plants is not to buy or plant them (and if they are growing on one’s property, to remove them) and to find native alternatives.
1 These definitions are found in Executive Order 13751 of December 5, 2016, Safeguarding the Nation From the Impacts of Invasive Species,
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References
Beaury EM, Patrick M, Bradley BA. August 2021. Invaders for sale: the ongoing spread of invasive species by the plant trade industry. Frontiers in Ecology and the Environment. 19(10): 550-556. doi: 10.1002/fee.2392
Gagnon J. April 29, 2020. Publication 420-320 (CNRE-105NP): Exotic Invasive Plants. Virginia Cooperative Extension. College of Agriculture and Life Sciences. Virginia Tech and Virginia State University.
[Note: VCE publications also has individual publications for various individual exotic invasive species, including English ivy, honeysuckle, Japanese barberry, periwinkle, and others available if you search the site for invasive species.]
Kudzu: The Invasive Vine that Ate the South. August 9, 2019. Stories in Indiana. The Nature Conservancy,
National Invasive Species Information Center. US Department of Agriculture. (accessed November 15, 2023).
Rawlins KA, Wallace RD, Moorhead DJ, Bargeron CT, Swain SJ. 2018. EDDMapS: Identifying and Mapping Invasives. The University of Georgia. Center for Invasive Species and Ecosystem Health, Tifton GA. BW-2018-01 32. (accessed November 15, 2023). EDDMapS- Early Detection and Distribution Mapping System.
Richmond J. Last reviewed January 2022. Native vs. Non-Native Plants. Extension: Invasive Species in Your Landscape. West Virginia University Extension.
Tongren S. Updated Feb. 15, 2023. “What is a Native Plant?” University of Maryland Extension. (accessed November 15, 2023).