New Invasive Plants on the Illinois Landscape

The challenge of invasive plant species is one of the most significant threats to native species and natural ecosystems in Illinois. Species such as bush honeysuckle, multiflora rose, common buckthorn and autumn olive are widespread and extremely damaging. Without a doubt, management of these species on both private and public lands is necessary to reduce their negative impacts.

Terry Esker, Regional Stewardship Coordinator for the Illinois Department of Natural Resources (IDNR) explained, “The negative impacts of invasive species on the natural communities located on IDNR lands cannot be overstated or underestimated. Of special concern are the impacts to high quality natural areas and Species of Greatest Conservation Need as identified in the Illinois Wildlife Action Plan. On IDNR lands, aggressive invasive species are changing the composition of the natural communities, which can result in the loss of native plant and animal species.”

On top of the overwhelming challenge of these established species are a suite of new invaders that are not yet widespread.

“Some of the new invasive species appearing on the Illinois landscape may be some of the most aggressive and difficult to control that private landowners and county, state and federal agencies have ever had to deal with,” Esker continued. Because of this, it is crucial to take advantage of the opportunity to take action to keep them in check before they become well-established and pervasive on the landscape. This has a far greater chance of success and return on investment.

What are some of these new invaders and which ones should we be on the lookout for? Here are four invasive plants that are present in Illinois, but not yet completely widespread.

Callery pear (Pyrus calleryana)

You may not have heard of Callery pear (a common cultivar is called Bradford pear) before, but I can guarantee you’ve seen one! Just drive around anywhere in Illinois in early spring and look for white-flowering trees growing in roadsides ditches or powerline rights-of-way. Almost always these are Callery pears. This species started out as a popular ornamental flowering tree with numerous varieties sold. While the flowering pear in your yard may look beautiful, the fruits they produce spread, with the offspring tending to revert to the wildtype species. Unfortunately, the wildtype species are shorter, more crooked, have smaller leaves and can actually grow quite large thorns.

While this species has been around Illinois for a long time, only within the last 20 or so years has this plant taken off and spread. Now, Callery pear are growing in almost any roadside or old field in Illinois. The fast-growing Callery pear real is a threat to young forests and tree plantings, where it can overwhelm young tree seedlings and rob them of light and space, and to prairie and grassland communities, where young seedlings can quickly dominate the landscape.

Amur corktree (Phellodendron amurense)

At first glance you may mistake Amur corktree for tree-of-heaven as both trees have compound leaves and a similar shallow diamond pattern to the bark. If you feel the bark of Amur corktree, however, you will find it is so soft that you can sink your fingernail into it. Hence the corktree name! You may also mistake corktree for an ash species since it has opposite branching and compound leaves. But female corktrees produce loose clusters of purple berries, which helps set this species apart from others. Also, peel back the bark of the corktree to reveal its unique lime-green to bright-yellow inner bark.

Corktree is occasionally still used as an ornamental plant and most escape populations can be traced back to nearby planted individuals. Recently, however, corktree has been showing up in forests, far from any known ornamental plantings. In particular, corktree seems to prefer sites with some disturbance, either from wind-storms or past logging.

Wineberry (Rubus phoenicolasius)

Wineberry does have one positive feature—it is one of the tastiest berries you will find in the wild! This exotic raspberry species has some characteristics that makes it easy to separate from Illinois’ native species. The first is the leaves, which are often separated into three to five leaflets and are bright white on the underside. The second is the dense, soft, red prickles that occur all over the plant, including the canes, leaf veins, and even on the fruit stems and bracts. This gives the entire plant a reddish, fuzzy look. Lastly, the berries are bright red in color when ripe.

The birds love those tasty wineberry fruits and will spread this plant across the landscape. Wineberry is not yet widespread in Illinois but is on the move and has been found in forests, riparian areas, roadsides and the edges of hill prairies.

Japanese chaff flower (Achyranthes japonica)

When it is not flowering or in fruit, Japanese chaff flower blends in with the other greenery in the forest understory. In late summer or early fall, the bottle-brush like flowers that sit in short spikes on top of the plant, or the fruit with pairs of short, pointed bracts that develop as the flower spikes elongate, make this species stand out. Those sharp bracts are also the mechanism for this species to spread as they hook onto anything that brushes up against them, taking a ride to a new location to further spread the species.

Japanese chaff flower made its way into Illinois relatively recently, being first found along the Ohio River in 2008. It has since spread into at least 17 counties in far southern Illinois. Some stands are so dense that they seem to be pushing out other invasive species that normally dominate, such as Japanese stiltgrass. The abundance of chaff flower on public lands, mixed with the popularity of southern Illinois as an outdoor recreation destination, heightens the risk of this species hitchhiking to other areas of the state.

Keep an eye out for these new invaders in Illinois. If you find them on public land, be sure to alert the land management agency. Controlling these species before they are widespread and well-established is crucial to successful land management.

• Illinois Department of Natural Resources’ Invasive Species site
• University of Illinois Extension Forestry Resources Invasive Species page
• University of Illinois Extension publication Management Guide for Invasive Plants and Pests of Illinois

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Chris Evans is an Extension Forestry and Research Specialist with the University of Illinois. A focus of his research and extension activities is invasive species management and forest health. Evans is currently a board member for the Midwest Invasive Plant Network, president of the southern chapter of the Illinois Native Society and a former board member of the North American Invasive Species Management Association and the National Association of Exotic Pest Plant Councils.