Science News for Kids:
What Makes a Plant an Invader?

When people move around the world, plants often travel with them, either on purpose or by accident. Historians think a plant called spotted knapweed came to North America from Eastern Europe around 100 years ago, probably because its seeds were mixed in with crop seeds that American farmers intended to plant. The spotted knapweed made itself right at home in its new environment, growing so fast that native American plants began to disappear. How could a single plant take over the landscape like that?

A team of scientists led by Harsh P. Bais of Colorado State University has discovered that spotted knapweed’s secret weapon is a poison that comes out of its roots and kills other plant species nearby. Back in Europe, other plants kept the spotted knapweed in check because over many years they had developed resistance to this poison. When the knapweed suddenly appeared on the scene in the United States, the native plants didn’t have this protection.

The news about this plant poison comes as a surprise. Scientists have generally believed that aggressive plants like the spotted knapweed succeed because they are better at using up resources like sunlight, water, and nutrients. This study may help researchers better predict whether new plant arrivals will get along nicely with their neighbors or turn into invaders like the spotted knapweed.

For more information, read Science for Kids. See also, Kids' Science News from AAAS.

—Kathy Wren

4 September 2003