Worst U.S. Invasive Species: Invasive Plants List
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How do we define invasive species? Learn about various U.S. invasive species and read our regional invasive plants list.
by Bruce Ingram
While recently walking through my 38-acre Virginia woodlot, I viewed much that was pleasing. A timber thinning had resulted in the oaks growing faster, expanding their crowns, and producing more acorns. A small clear-cut had let more sunlight reach the forest floor, causing native blackberry, dewberry, and raspberry vines to thrive and provide more berries for wildlife and my wife, Elaine, and me.
Regardless of my hard work, I also observed much that was displeasing. For despite my years-long battle against them, invasive plants appeared everywhere. Multiflora rose has a foothold in the edge habitat of my hardwood hollow. Autumn olive grow all along my seeded logging road, and sericea lespedeza live inside the byway in places. And garlic mustard, Asiatic bittersweet, and Japanese stilt grass and Japanese honeysuckle (as well as other invasive plants) appear across the landscape.
U.S. Invasive Species Threaten Native Flora and Fauna
Dr. Stephanie Frischie is the native plant materials specialist for The Xerces Society (a science-based organization protecting wildlife through the conservation of invertebrates and their habitats). She acknowledges the threat that native plants and animals face from invasive plants.
“By definition, invasive plants are non-native ones that aggressively outcompete and displace native flora,” she says. “If an invasive invades and becomes dominant, native birds, insects, and other animals may well lose many of their food sources, breeding habitats, and winter shelter areas.
“Invertebrates, such as bee species, butterflies, moths, and other pollinators, are extremely important for agriculture from major growers to backyard gardeners. Pollinators need native plants to feed and lay their eggs on. If our native flowers largely disappear from an area because of invasive plants, then that’s a major loss to humans and the food chain.”
Worst Invasive Plants List: East
Cully McCurdy, a National Wild Turkey Federation district biologist, covers some of the worst invasive plants in the eastern U.S.
“The problem with invasive plants in the East, and really anywhere in the country, is that, many times, native plants can’t compete with them,” he says. “The reason why is that some of the worst ones in the East, like multiflora rose and autumn olive, often form monocultures where few other plants can grow. The invasive plants, once established, just choke out the natives.”
McCurdy says major invasive plants in the eastern U.S. include garlic mustard, Japanese stilt grass, Japanese honeysuckle, Chinese privet, ailanthus, knotweed, mile-a-minute weed, and kudzu — and this is just the beginning of a very long list.
Rogues Gallery: Midwest and West
Frischie relates that in the Midwest, some of the most challenging invasive flora to deal with include amur honeysuckle, buckthorn, reed canary grass, and Canada thistle. Notable others include bush honeysuckle, sericea lespedeza, and Russian olive. McCurdy adds red cedars to that rogues’ lineup. Though a native tree in the East, this evergreen has proven to be one of that region’s worst invaders, frequently outcompeting native flora. Japanese bush honeysuckle and Chinese privet are problems here, too, just as they are in the East.
Out West, some of the worst scourges, continues Frischie, include yellow star-thistle, Himalayan blackberry, cheat grass, and spotted knapweed. Bush honeysuckle, sericea lespedeza, and Russian olive can also wreak havoc, environmentally.
The native plants specialist says that every state’s website contains information on the invasive plants found there, as well as treatment options.
Individual Invasive Plants of Note
Some invasive plants are so destructive, widespread, and hard to kill or control, that they achieve special infamy. Blanketing most of the eastern half of the country, autumn olive, an Asian native, certainly qualifies as one such species. This shrub’s two easiest to identify traits are the leaves and berries. The leaves are lance-shaped and between one and three inches long; the sun-exposed side of the leaves are dark green and the undersides are silver. If I’m ever confused whether a shrub is an autumn olive or not, I just flip the leaves over and look for a flash of silver.
The red berries are sweetly tart, and some people make jam from them. Many native animals never or rarely consume the fruits of some invasive plants; unfortunately, that’s not the case with autumn olive, as numerous species of birds relish them. This situation, of course, enables the autumn olive to quickly spread through an area … courtesy of songbird poop.
One final trait of note is the suffocating, sweet smell the blooms emit in the spring. That aroma can be overwhelming in a vast stand of autumn olives, which leads to another issue regarding this plant. It forms vast monocultures where nothing else can grow.
Multiflora rose is another infamous plague. Like the autumn olive, it thrives across the eastern half of the country, but this rose has also managed to gain a foothold in the Pacific coastal states. Its most salient feature are long, curved, vicious thorns. Trying to walk through a multiflora rose copse is an impossible task, as those thorns seem to reach out and rip skin and clothes. Native plants likewise find these thickets impenetrable, as rose stands readily form desert-like thickets where nothing else grows.
Ground ivy doesn’t flaunt thorns or pretty red fruits like our previous two non-natives, but it’s one of the most rapidly spreading, monoculture forming, garden-ruining plants I’ve ever dealt with. Six years ago, we had never seen this plant in our yard or garden — now it has overrun both, and, because of it, we decided to raise our vegetables in raised beds from now on.
Ground ivy now thrives throughout the vast majority of the Southern states and forms dense, ground hugging, foul smelling mats. The circular, scalloped leaves are diagnostic, and the purple flowers aid in identification come spring.
More Information on Invasive Plants
Read more about how to battle and stop invasive plants in the article: How to Control Invasive Plants on the Homestead.
Bruce Ingram is a freelance writer and photographer. He and wife Elaine are the co-authors of Living the Locavore Lifestyle, a book about living off the land. Get in touch with them at BruceIngramOutdoors@gmail.com.
Originally published in the March/April 2024 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.
