University of Vermont Extension
Department of Plant and Soil Science

News Article

Invasive Exotic Plants

By Dr. Leonard Perry, Extension Professor
University of Vermont

Man-eating plants? Alien plants from Mars out to conquer the world? No, the plants now called "invasive exotics" may already be in your garden!

Invasive means just that--they invade where they're not supposed to. This can be by self-sowing seeds, such as with hollyhocks and poppies, or by creeping roots--mint being the best example of this. In the bigger landscape outside your own garden and yard-- the natural community such as fields and forests-- invasive plants may not be desirable as well.

Often invasive plants aren't desirable in natural settings if they've been introduced by human activities, such as from the early settlers. Sometimes his has been intentional, other times unintentional as seeds are inadvertently transported on cargo and in ballast of ships. Native plants are defined differently by different groups, but generally are considered those plants found growing in an area at least 100 to 300 years ago. Plants introduced since then are often termed "exotic". So those introduced plants, which are also invasive, are called "invasive exotics."

So why is all this important? Natural communities of plants (and animals too for that matter) are generally in balance, with all the many species coexisting. Exceptions seem to be areas, such as forests, that one species, such as maple, dominate. But even then, if you look closely, many other species of plants may be present.

The problem comes when a plant not originally found in one of these plant communities is introduced from elsewhere and acts as a "bully" and takes over. It often displaces and kills other native species that certain wildlife need to survive. Loss of native species sometimes leads to a wildlife species becoming endangered or extinct.

Invasive exotics may completely change a habitat, especially in the case of wetlands. This is where invasive plants are often found, as the seeds and even root and plant pieces are carried down streams and into lakes by the water.

Examples of invasive exotic plants you may know from gardens are the Purple Loosestrife (Lythrum salicaria), shrubby honeysuckles (Lonicera), Russian Olive (Elaeagnus), Buckthorn (Rhamnus), Goutweed (Aegopodium), or Yellow Flag Iris (Iris pseudacorus). Even though some of these are quite attractive, they are documented as causing problems as noted above.

Some varieties or cultivars (cultivated varieties) of invasive exotic plants may not spread, or may not be spread by seeds, wind, or birds. Or, perhaps, these non-spreading cultivars cross with the spreading species, and so end up causing problems. This is the case with the Purple Loosestrife, which explains why it (even the cultivars) is banned from sale in many states.

Vermont does not legally ban invasive plants, but there is a committee set up to study which may be problems, and to provide information through fact sheets and other means. This committee gets input from several agencies and organizations. Its information can be accessed through the Vermont Department of Environmental Conservation, 102 South Main St., Building 10 North, Waterbury, VT 05671-0408 (phone 802-241-3777). Ask for the free booklet on invasive plants, which provides specific information on individual species and how to deal with them.

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