Invasive Species

What is a Non-native Plant?

Non-native plants (also called non-indigenous plants, invasive plants, exotic species, or weeds) are plants that have been introduced into an environment in which they did not evolve. Introduction of non-native plants into our landscape has been both accidental and deliberate. Purple loosestrife, for example, was introduced from Europe in the 1800’s in ship ballast and as a medicinal herb and ornamental plant. It quickly spread and can now be found in 42 states where it chokes streams and crowds out almost every other species of stream bank and wetland plant.


In general, aggressive, non-native plants have no enemies or controls in their new environment to limit their spread. As they move in, the existing complex native plant communities, with hundreds of different plant species supporting wildlife, will be converted to a monoculture. This means the community of plants and animals is simplified, with most plant species disappearing, leaving only the non-native plant population intact. Along with the impact on plant species is a concurrent impact on animal life.  Many insect species (bees, butterflies, as well as others) are adapted to specific native plants as food sources.  When invasives take over, the overall population of insects and the diversity of insects drops dramatically.   While this may sound good to those who do not like insects, it is terrible news for the frogs, toads, and birds whose food source is this diminished insect population. [Birds, even those that you think of as seed eaters, require substantial insect additions to their diet when raising their young, as insects are the prime source of protein for the growing nestlings.] Please think before you plant!  There are many species like teasel, purple loosestrife, reed canary grass, European buckthorn, tartarian honeysuckle, garlic mustard, among others that cause our native populations to be overrun. If you are not certain of the invasive nature of a plant, ask or check out the many web sites that provide information on these plants.  A list of plants considered invasive in Illinois can be found at:



Teasel is endemic to Europe. It was introduced to North America possibly as early as the 1700’s. Teasel has spread rapidly in the last 20-30 years. Teasel grows in open sunny habitats, ranging from wet to dry conditions. Teasel sometimes occurs in high quality prairies, savannas, seeps, and sedge meadows, though roadsides, dumps, and heavily disturbed areas are the most common habitats.

A single plant can produce up to 6,000 seeds.
Depending on conditions, up to 30-80% of the seeds will germinate, so each plant can produce many offspring. Seeds also can remain viable for at least 2 years and up to 10 years. Seeds typically don’t disperse far by themselves, so most seedlings will be located around the parent plant. Parent plants often provide an optimal nursery site for new teasel plants after the adult dies. However, mowing seed-bearing plants spreads the seed far and wide, where they will germinate on any bare, sunny spot of ground.

Teasel Identification
Teasel grows as a basal rosette for a minimum of one year then sends up a tall flowering stalk and dies after flowering. Common teasel blooms from June through October.

Click the image to learn how to control teasel.

Image of mature teasel stalks.

Mature seed heads. The plant has dropped its seeds.