Other examples are "Centaurea solstitialis" (yellow starthistle) and "Centaurea diffusa" (diffuse knapweed). These Eastern European noxious weeds have spread through the western and West Coast states. Experiments show that 8-hydroxyquinoline, a chemical produced at the root of "C. diffusa", has a negative effect only on plants that have not co-evolved with it. Such co-evolved native plants have also evolved defenses. "C. diffusa" and "C. solstitialis" do not appear in their native habitats to be overwhelmingly successful competitors. Success or lack of success in one habitat does not necessarily imply success in others. Conversely, examining habitats in which a species is less successful can reveal novel weapons to defeat invasiveness.