Invasive Plant Species

by Christa Partain

I spent my first 19 years in the South and have the pleasure of getting back to my home state of Arkansas about once a year to visit my mom (a Master Gardener). During my annual pilgrimage, I take the time to travel through the state to visit my aunt (also a Master Gardener) or to go botanizing. What has struck me is the relative absence of invasive plants, especially compared with the Mid-Atlantic, where I have lived for the past 20 years. (The southern portion of the Gulf States is an exception.)

According to the Ecological Society of America, an exotic invasive plant is a "non-indigenous species that evolved elsewhere and has been purposely or accidentally relocated. Invasive species are a subset of introduced species that persist, proliferate, and cause economic or environmental harm or harm to human health." Okay, so what's the big deal?

On a global basis ... the two great destroyers of biodiversity are, first, habitat destruction, and second, invasion by exotic species. (E.O. Wilson).

Invasive species have contributed directly to the decline of 42 percent of the threatened and endangered species in the U.S. (Travaglini, 2009).

Introduction of species is perhaps the most permanent and unrecoverable blow to native biodiversity and ecosystem processes and integrity (Westbrooks, 1998).

To date, over 5,000 alien plants have invaded the natural areas of North America (Tallamy, 2007). Non-indigenous weeds are spreading and invading approximately 700,000 hectares of U.S. wildlife habitat per year (Pimentel, et al 2005).

The estimated damage from invasive species worldwide totals more than $1.4 trillion - 5 percent of the global economy (Pimentel, et al 2001).

The annual cost to the United States economy is estimated at $120 billion a year (Travaglini, 2009).

Studies indicate that up to 83 percent of the total number of invasive taxa (species, varieties or cultivars) in the U.S. had a horticultural origin. This tells us gardeners that we need to be very careful about what we plant in our gardens. Kudzu and golden bamboo are infamous examples. If you are wondering about a specific plant, check out

If the plant you are considering is an invasive in a part of the country that has a similar climate to yours, please don't plant it. It is irresponsible to introduce such a plant - in a couple of years the plant will be on your state's invasive plants list because just a few people gave it a foothold. As my Master Gardener aunt says, "[Plants] that self-sow or spread aggressively annoy me greatly! Let them into your garden at your own peril," and, unfortunately, at the larger ecosystem's peril.

Some horticulturists recommend limiting the use of such aggressive plants to areas where they can be controlled. The problem with this reasoning is that birds, the wind, people, cars and other dispersal agents can spread the seeds or even vegetative pieces of the plant to colonize outside your garden. As a gardener, you have probably witnessed the miraculous spread of an unwanted species firsthand.

It is so much easier to prevent the introduction of an invasive organism than it is to eradicate it. Invasive plant pulls are hard work. If you want to get a taste of one, I'm sure the people at your state's Heritage Program know of some sites that could use a little cleaning up.


(Click on any photo to enlarge)

Christa Partain is Senior Horticulturist and Plant Ecologist at the National Aquarium in Baltimore. She has a Master of Science in Environmental Biology, with a concentration in plant ecology, from Hood College. Christa has 15 years of experience in horticulture, most of which is in public horticulture. She also teaches horticulture classes at the USDA Graduate School. Christa is an active member of the Botanical Society of Washington and the Maryland Native Plant Society, and is involved with other plant conservation organizations.


Works Cited

* Pimentel, D., R. Zuniga, and D. Morrison. 2005. "Update on the environmental and economic costs associated with alien-invasive species in the United States." Ecological Economics 52(3):273-288.

* Pimentel, D., S. McNari, J. Janecka, J. Wightman, C. Simmonds, C. O'Connell, E. Wong, L. Russel, J. Sern, T. Aquino, and T. Tsomondo. 2001. "Economic and environmental threats of alien plant, animal, and microbe invasions." Agriculture, Ecosystems, & Environment 84 (1):1-20.

* Tallamy, D. 2007. Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. Portland: Timber Press.

* Travaglini, Mary. "Complicating Factors in Invasive Plant Management: Circumstances Beyond our Control?" Mid-Atlantic Exotic Plant Pest Council's annual conference. Johnstown, Pennsylvania. August 12, 2009.

* Westbrooks, R. 1998. Invasive plants, changing the landscape of America: Fact book. Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW), Washington, D.C.


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