Invading plant species, such as the Centaurea, establish monocultures in novel habitats by displacing the indigenous plant communities. It is thought that the absence of "natural enemies" and/or the release of phytotoxins from the invading plants by allelopathy promote this process. Previous work has shown that the European spotted knapweed (Centaurea maculosa) releases racemic catechin; the phytotoxin (-)-catechin, and the antimicrobial (+)-catechin. Invasive (-)-catechin levels in North American soil were found to be more than double those found in the natural habitats of C. maculosa. In the September 5 Science, Harsh Bias and colleagues at Colorado State University show that (-)-catechin inhibits growth of a number of nature North American plants by altering gene expression, resulting in extensive root death (Science, 301:1377-1380, September 5, 2003).