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Invasive Plants and Animals

Watch for the following invasive species and whenever possible, remove them from our woodland environment.

Gardeners Beware! You might be surprised to learn that some plants considered to be invasive in Illinois may be sold at our local nurseries, or passed along from gardener to gardener. We commonly plant the offenders in our gardens, particularly because they are so easy to grow. Unfortunately, if they "escape" to the woodlands or prairies, they can become difficult to remove. It's best not to plant them in your garden at all, but if you do, watch that they don't spread into native areas. Here is a list of some plants to avoid, or carefully control:

Buckthorn (Rhamnus spp.)

There are two species of buckthorn found in Riverwoods. Rhamnus cathartica, the Common Buckthorn pictured here, is in fact, the most common. This small tree or shrub leafs out early in the spring and doesn't drop all of its leaves until very late in the fall. Their dense shade throughout the growing season will not allow native plants to survive. Mature buckthorn will produce branches filled with seeds that fall to the ground or are spread by birds, planting new buckthorn everywhere. The other species, Rhamnus frangula, is more often found in wetlands or open moist areas. Either species can be controlled by cutting and painting the stump with herbicide. Additional spraying may be necessary in the spring. This is a good fall activity because it is easy to identify the buckthorn when it is the only shrub or tree left with leaves. It's a good winter activity too -- no bugs, no rain and a good time to burn.

Learn more about buckthorn at The Minnesota Department of Natural Resources
or The University of Minnesota Extension Service. For a video by the Wisconsin DNR on identifying and controlling buckthorn, Click Here.

An RPC article in the January / February 2006 issue of the Village Voice contains extensive information. Other good sources are: the US Forest Service, Wisconsin DNR, the University of Wisconsin, the Invasive Plants Association of Wisconsin, the Village of Lincolnshire, the Minnesota DNR, and the Plant Conservation Alliance.

Canada Thistle (Cirsium arvense

Common Teasel is found in sunny areas and is marching across America along the highways and byways of the country. This prickly plant establishes thick stands along roads, in pastures and in the open meadows of our forest preserves.

Teasels are biennials, like Garlic Mustard, starting with a rosette of leaves close to the ground the first year, and shooting up over 6 feet tall the next year, when they produce multiple purple flowers. Flower heads can produce over 3,000 seeds per plant, so if you see one growing on your property, remove it asap. Stems are so prickly, it's hard to touch them at all, but they do add interest to arrangements of dried flowers ...which is about the only good thing about them! A cutleaf version is found in wet areas.
Learn more about Common Teasel at the Illinois Natural History Survey web site.

(photo courtesy of the Virginia Tech Weed Identification web site)

Creeping Charlie, sometimes called Ground Ivy, is usually thought of as a common nuisance lawn weed that is difficult to control. Unfortunately, it has also spread to natural areas, particularly moist shady areas like those in Riverwoods. Very large colonies can be seen near the Des Plaines River. In the spring, the plant produces small purple flowers. By fall, the plant colonies grow, as stems reach out and root into the ground.

The U. of Wisconsin Dept. of Horticulture has a good discussion of Creeping Charlie, with photographs. Click Here for a short article about control of Creeping Charlie by the U. of Illinois Extension Service.

Garlic Mustard is a biennial, a plant with a two-year life cycle. The first year seedlings are small rosettes, close to the ground. The second year, plants grow up to 3 feet tall, producing many small flowers and long thin seed pods. Removing stands of garlic mustard is a challenge. To bring it under control, several years of patient eradication is needed. But the results will be worth the efforts required. Learn more about Garlic Mustard and options for control at the Plant Conservation Alliance and Illinois Natural History Survey web sites. The Stewardship Network has prepared an excellent video on garlic mustard. The video, created by Barbara Lucas and funded by Wisconsin Family Forests, dramatically illustrates the problem of garlic mustard, management techniques, and the benefits of eradication. To view, Click Here. To see another video, by the Wisconsin DNR, Click Here.

The RPC published an article on garlic mustard in the January / February 2006 issue of the Village Voice. Other sources include: the Wisconsin DNR, the Invasive Plants Association of Wisconsin, the University of Wisconsin, Dr. John Hilty's Illinois Wildflowers web site, and the Plant Conservation Alliance.

Egg masses with newly hatched larva	4th stage larva	5th (final) stage larva	Pupa	Male and female adult moths	Female with egg case

Indian Strawberry (Duchesnea Indica)

You may notice new strawberry plants spreading through your property. Check them carefully -- if they have yellow flowers and hollow, tasteless berries, they are Indian Strawberry. Our native strawberries have white flowers and if the birds don't eat them first, and there are any left for you to try, they are tiny and sweet.

Indian Strawberry is beginning to spread in Riverwoods. Once it takes hold, it becomes difficult to remove, so pull them or treat them with RoundUp® as soon as you find them. This is not a good groundcover!

Indian Strawberry is on the Chicago Botanic Garden list of invasive plants in the midwest.

Photo: Bodner, Ted. Southern Weed Science Society. www.invasive.org

Japanese Barberry (Berberis thunbergii)

Japanese Barberry was introduced to the United States as an ornamental shrub, living fence and for erosion control. It is a small, compact, spiny bush with green, gold or red leaves. The gold and dark red varieties look beautiful against the greens that dominate our landscapes and deer avoid the prickly bushes. But birds have spread the little red berries of the Japanese Barberry plants from the east coast throughout the midwest. Although in Riverwoods they dot the woodlands here and there, they are now found in Eastern oak forests forming thick stands that dominate the woods. Don't compound the problem by planting more. If you have Japanese Barberry in your woodland, please remove the plants. Learn more about Japanese Barberry at the Minnesota DNR or the Southeast Exotic Pest Plant web site.

Moneywort / Creeping Jenny (Lysimachia nummularia)

Moneywort, sometimes called Creeping Jenny, is flourishing in many parts of Riverwoods, particularly near the Des Plaines River and other moist areas. It sprawls over the ground, creating a thick, dense carpet of leaves even in the shadiest places. In the end of June and beginning of July, yellow flowers appear. This plant does not provide nectar for butterflies or fruit for birds, is bitter tasting to mammals, smothers out any native plants that try to grow where it is established and is a European import to remove!

A gold variety is sold for gardens. It's best not to plant Creeping Jenny in Riverwoods, but if you do, be careful to watch that it doesn't spread into the woods. With its small breakable roots, it is very difficult to eliminate.

Learn more about moneywort at the Illinois Wildflowers web site.

Purple Loosestrife (Lythrum salicaria)

Purple Loosestrife is a beautiful perennial that forms dense stands in moist open areas. From June through August, you can see its magenta flowers blooming along many of our highways and filling fields with brilliant color. Not surprisingly, it was introduced in the 1800's as a garden plant and herb and also arrived as seeds in the ballast of ships and the wool coats of sheep. Unfortunately, purple loosestrife has made itself at home here, taking over areas to the exclusion of other plants and reducing habitat for wetland animals and birds. Illinois has had some success in experimental areas controlling the plant using species-specific beetles. If you have purple loosestrife on your property or in your garden, remove it. The State of Illinois outlaws the sale of purple loosestrife and it is even on the list of plants eBay will not allow to be sold on its site.

Learn more about purple loosestrife at the Plant Conservation Alliance and Illinois Natural History Survey web sites.

Poison Ivy

Poison Ivy is an extremely common plant in Riverwoods. It is easily recognized by its three leaves growing from a single stem, two of which are shaped like opposed mittens. Reaction to poison ivy can be very serious. The three basic rules are: (1) Don't touch it at any time of year, (2) carefully wash any clothes or implements that do touch it, and (3) never burn poison ivy, since the smoke can cause severe lung irritation. For a detailed discussion, see the RPC's article in the May / June 2007 issue of the Village Voice.

Emerald Ash Borer

The RPC published articles on the emerald ash borer in the July / August 2006 and September / October 2007 issues of the Village Voice. The Illinois Department of Agriculture web site also discusses the emerald ash borer.

General information about invasives: There is a lot of information available on the web. Three good sites with photos are: the Minnesota DNR, the Wisconsin DNR, and the Chicago Botanic Garden. Chicago Wilderness has lots of info from the largest alliance of natural areas in the Chicago region. The Midwest Invasive Plant Network and the Wisconsin Department of Natural Resources have a lot of detailed information about invasives. The Illinois Department of Resources and the United States National Arboretum are also very good resources.

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