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.

Some highly invasive plants in North America with chemical compounds not found in native species.
Common Name Scientific Name Unique Chemical Chemical's Properties
Brazilian peppertree Schinus terebinthifolius schinol toxic to mammals and birds
Dalmatian toadflax Linaria dalmatica linarioside kills roundworms
Garlic mustard Alliaria petiolata alliarinoside prevents insects from feeding and impedes their growth
Gorse Ulex europaeus maackiain antifungal and antimalarial
Japanese knotweed Polygonum cuspidatum piceid inhibits fungi and bacteria, prevents browsing
Leafy spurge Euphorbia esula esulatin toxic to some mammals
Pale swallow-wort Vincetoxicum rossicum antofine destroys cells and inhibits fungi
Russian knapweed Acroptilon repens cnicin toxic to insects, plants and fungi
Spotted knapweed Centaurea biebersteinii catechin poisonous to plants

Naomi Cappuccino and J. Thor Arnason. 2006. Novel chemistry of invasive exotic plants. Biology Letters. 2(2): 189-193.

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