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Escape of the invasives: Top six invasive plant species in the United States

By Emily Grebenstein

Non-native plant species pose a significant threat to the natural ecosystems of the United States. Many of these invasive plants are escapees from gardens and landscapes where they were originally planted. Purchased at local nurseries, wholesale suppliers and elsewhere, these plants have the potential of taking over large areas, affecting native plants and animals and negatively changing the ecosystem. In recent years an increase in travel and international trade has rapidly introduced many new non-native species to the United States.

“While not all non-native plants are bad, some imported species are bullies that crowd out native plants and damage the diverse ecosystems that many living things depend on,” said James Gagliardi, a horticulturist with Smithsonian Gardens.

Plants with the highest invasive potential are prolific seeders and vigorous growers which have the ability to adapt well to a variety of conditions. Native species have not evolved alongside these plants and have trouble competing. With few predators and little competition for resources, these new plants can displace native flora, reducing plant diversity until a landscape is no longer able  to support longstanding native plant, animal, and insect communities.

Here is James Gagliardi’s top six list of the most prolific plant invaders in the U.S. with suggestions of native stand-ins to plant in your garden:

1. Purple Loosestrife (Lythrum salicaria)

Origin: Europe and temperate Asia


(Photo by John D. Byrd, Mississippi State University,

Arrival: Purple loosestrife was introduced to the United States in the early 1800s for ornamental and medicinal uses.

Impact: Now growing invasively in most states, purple loosestrife can become the dominant plant species in wetlands. One plant can produce as many as 2 million wind-dispersed seeds per year and underground stems grow at a rate of 1 foot per year.

Native Alternatives: Blazing star (Liatris spicata), American blue vervain (Verbena hastate) and New York ironweed (Vernonia noveboracensis)

2. Japanese Honeysuckle (Lonicera japonica)

Origin: Eastern Asia


(Photo by Charles T. Bryson, USDA Agricultural Research Service,

Arrival: One of many invasive varieties of honeysuckle in the United States, Japanese honeysuckle was brought to Long Island, NY, in 1806 for ornamental use and erosion control.

Impact: The plant has become prolific throughout much of the East Coast as it adapts to a wide range of conditions. Japanese honeysuckle is an aggressive vine that smothers, shades and girdles other competing vegetation. Many of the birds eat the fruit of this plant, thereby spreading the honeysuckle’s seeds.

Native Alternatives: Trumpet creeper (Campsis radicans) and coral honeysuckle (Lonicera sempervirens)

3. Japanese Barberry (Berberis thunbergii)

Origin: Japan


(Photo by Leslie J. Mehrhoff, University of Connecticut,

Arrival: Japanese barberry was introduced to the United States in the 1800s as an ornamental. Seeds of Japanese barberry were sent from Russia to the Arnold Arboretum in 1875 as an alternative to European barberry (Berberis vulgaris), which had fallen out of favor as it was a host to Black Rust Stem—a serious fungus effecting cereal crops.

Impact: The shrub has the ability to grow in deep shade and is particularly detrimental to forest lands in the Northeast. The heavily fruiting plant forms dense thicket, crowding out native plants, and its seeds are easily spread by birds.

Native Alternatives: Shrubby St. Johnswort (Hypericum prolificum) and winterberry (Ilex verticillata)

4. Norway Maple (Acer platanoides)

Origin: Europe


(Image by Zelimir Borzan, University of Zagreb,

Arrival: The plant explorer John Bartram first introduced the Norway maple to the United States from England in 1756. The widely adaptable tree quickly became popular and was planted in towns as a shade tree and in rural communities.

Impact: The Norway maple displaces native trees and has the potential to dominate a landscape in both the Northeast and Northwest. It displaces native maples like the sugar maple and its dense canopy shades out wildflowers.

Native Alternatives: Sugar maple (Acer saccharum) and red maple (Acer rubrum)

5. English Ivy (Hedera helix)

Origin: Europe


(Photo by Chris Evans, Illinois Wildlife Action Plan,

Arrival: The introduction of English ivy dates back to the early 1700s when European colonists imported the plant as an easy-to-grow evergreen groundcover.

Impact: The planting and sale of English ivy continues in the United States even though it is one on the worst-spread invasive plants in the country due to its ability to handle widespread conditions, particularly on the east and west coasts. English ivy is an aggressive-spreading vine which can slowly kill trees by restricting light. It spreads by vegetative reproduction and by seed, which are consumed and spread by birds.

Native Alternatives: Creeping mint (Meehania cordata), Allegheny spurge (Pachysandra procumbens) and creeping phlox (Phlox stolonifera)

6. Kudzu (Pueraria montana var. lobata)

Origin: China, Japan and the Pacific islands 


(Photo by Kerry Britton, USDA Forest Service,

Arrival: Japan introduced Kudzu to the U.S. at the Philadelphia Centennial Exposition in 1876. It was first promoted as an ornamental plant and later as a forage crop in the Southeast. One million acres of Kudzu were planted in the 1930s and 1940s by the Soil Conservation Service to reduce soil erosion on deforested lands. It was not until the 1950s that it was recognized as an invasive.

Impact: Once established, Kudzu grows at a rate of up to one foot a day and 60 feet annually. This vigorous vine takes over areas in the Southeast by smothering plants and kills trees by adding immense weight and girdling or toppling them.

Native Alternatives: Carolina jessamine (Gelsemium sempervirens) and Virginia creeper (Parthenocissus quinquefolia)


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  • Phil Hoffman

    Marin County Ca. is being invaded by Cape Ivy (Delairea Odorata) which is obliterating native landscapes within months. It should be high up on the list.

  • Matt Chew

    Judged by their areas of comprehensive ecosystem replacement the top four introduced plant species in North America are corn, wheat, soybeans, and cotton. Other row crops and lawn grasses like ‘Kentucky’ (actually English) bluegrass and Bermuda (actually African) grass follow. Their ‘invasions’ have what the ‘feral’ plants listed in this article critically lack: intention and coordinated action to take and hold territory. It’s obviously not their own intention, because, well, they’re plants. They have no idea of ‘here’ or ‘there,’ of where they are or where they belong. They survive (or not) under prevailing conditions. We intentionally make (or suppress) those conditions. If there is an ‘invasion’ at all it is our invasion. It is absurd to vilify any plant for growing under the conditions to which it is adapted, or demonize a plant population for rapidly evolving adaptations to formerly marginal conditions. But if we’re going to accept the idea of plant invasions it is equally absurd to exempt those that happen to be serving someone’s economic interests. It all boils down to whether a particular kind of plant has human proponents or opponents. Enough of a constituency ‘for’ or ‘against’ justifies industrial-scale killing of something-or-another, and the plant-killing industry eagerly exploits and ‘cultivates’ those constituencies. Seen in that light, this isn’t even about ecology. It’s ultimately about who can convince you to buy what they have for sale, and accept the ensuing collateral casualties as the normal costs of doing business.

    • Anon Ymous

      ^^ This. More info please on organizing to break the cycle? How to get people to see the hypocrisy of glyphosating the invasives to a death that does not stop at the root?

      • Matt Chew

        I attempted to reply. Apparently my reply was censored.

        • Anon Ymous

          Hmmm. I found your comment because I was searching for exactly this level of theory on horticultural economics. Thanks for the well written summary. I want to organize locally to help people see the bigger picture, but for many around here, seeing means biting the hand they believe is feeding them. Emphasis on believe. And the corporate trolls don’t limit themselves to online forums.

          • Matt Chew

            Apparently any reply including a URL is rejected- even if it is a Smithsonian page! Bots are idiots. Google my name and get in touch.

          • Anon Ymous

            Found you and will do. Thanks.

    • David Franklin

      Dude you’re weird

      • Matt Chew

        I see you’ve put a lot of thoughtful effort into understanding the situation. Thank you for that insight.

  • I have three of these, plus wisteria in my yad. Our Norway maples are mature and beautiful, plus their ‘helicopter’ pods provide one of the few wild foods our squirrels and some other animals have left to live on, with the encrouching human species ( let’s be honest – we’re the ultimate invasive species). We do our best to control the ivy and wisteria and confine the honeysuckle to climbing on our fence.

  • wisteria is beginning to rival kudzu in southern US states. It can be stunningly beautiful for a month out of the year, but it spends the rest of the time rapidly growing and strangling other plants.

  • Lawton Thomas

    Scotch Broom is a beautiful flowering plant. It is widespread, not only in the north west, but also Spain and southern France. Until I saw it growing in Seattle, I assumed it grew in semi-arid areas.

  • James Shultis

    Scotch Broom is the scourge of the Pacific Northwest.

  • Janie

    Kudzu is everywhere

  • Marni Majorelle

    they should ban barberry from being sold at nurseries!

  • Lisa Cihlar

    Garlic mustard has taken quite a toll on the wildflower population here in the midwest.

  • Stanton_Park

    … Black Rust Stem—a serious fungus effecting affecting cereal crops… …sale of English ivy continues in the United States even though it is one on of the worst-spread invasive plants…

  • Jill Boniske

    You might mention that the kudzu bug has followed the vine and is wreaking havoc on agriculture all over the South.

  • Hmm, buckthorn didn’t make the list?

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