Invasive Plants - U of I Extension

News Release

Invasive Plants

This article was originally published on July 23, 2010 and expired on December 31, 2010. It is provided here for archival purposes and may contain dated information.

Roadways and highways are becoming one of the major pathways by which invasive plants spread. An invasive plant is one that has the ability to thrive and spread aggressively outside its natural range. A naturally aggressive plant may be especially invasive when it is introduced to a new habitat.

So be on the lookout for invasive plants lurking along highways and interstates. Wind and air movement from passing vehicles help disperse seeds. Cutting and mowing, and regular road maintenance activities can aid in the spread of these invasives.

This column will mention some of the invasive species in Illinois, particularly those you may notice while travelling on roads. There are more invasive plants than those listed here; and remember, there are many native species along Illinois roadsides as well.

Common teasel is a purple flowering plant that may reach 6 to 7 feet in height. While beautiful to look at, it does not take long for this plant to quickly form a monoculture that excludes all natural vegetation. Teasel plants produce over 2,000 seeds per plant and the seeds get spread by mowing along roadways.

Spotted knapweed has a very deep tap root that may aid in soil erosion and surface runoff. It releases toxins that prevent native plants from growing, making restoration difficult. Flowers are purple to pink in color and occur on small flower heads.

Autumn olive can be identified by the underside of its leaves that are silvery and dotted; it produces yellow flowers and red fruits. This plant was introduced to control erosion but tends to crowd out native plants.

Tree-of-heaven grows rapidly and establishes in dense stands (like autumn olive). It overruns native vegetation and produces toxins that prevent native growth. Tree of heaven resembles the sumacs and hickories, but is easily distinguished by the glandular, notched base on each leaflet and large leaf scars on the twigs.

Poison hemlock forms dense stands along roadways and in ditches. Stems are hollow, ribbed, and purple-spotted. While it grows quickly and displaces native plants like the plants listed above, it also can harm people. All parts of the plant are poisonous and the plant sap can also irritate the skin, causing rashes. It is also poisonous to livestock.

Pictures of the above mentioned invasive plants can be found in the University of Illinois Home, Yard, and Garden Pest Newsletter, July 16, 2010 issue, available at this web site Another reference is the Center for Invasive Species and Ecosystem Health, see this web site

Source: Jim Morrison, Extension Educator, Crop Systems,

Pull date: December 31, 2010