Chemical Arsenal Helps Plants Invade

Biologists probing the question of why some exotic plants can quickly populate a continent have uncovered another characteristic of successful invaders. Among 21 species, considered as some of the most invasive plants in North America, nearly half (43 percent) produce a potent chemical that is not found in any native vegetation.

In contrast, only 11 percent of common North American plant species contain unique chemicals.

Plants use these chemicals to ward off leaf-eating insects, pathogenic microbes, or even browsing mammals. A study showing that insects do significantly less damage to leaves of invasive plants which contain compounds unique in North America demonstrates the protective value of having uncommon chemistry.

Not all the compounds serve to escape enemies. Some chemicals exuded from roots are allelopathic. They act on the offensive by being poisonous to other kinds of plants, thereby reducing competition.

The chemicals created by invasive species are not necessarily more noxious than those found in native flora. Their effectiveness lies in being new to the organisms that would otherwise damage the foreign plants. Local insects, diseases, animals and plants have not yet adapted to overcome the particular challenges these new chemicals pose.