A test of Darwin's naturalization hypothesis in the thistle tribe shows that close relatives make bad neighbors

Significance Invasive species negatively impact both natural ecosystems and human society and are notoriously difficult to control once established. Thus, identifying potentially invasive taxa and preventing their dislocation is the most efficient management method. Darwin’s naturalization hypothesis, which predicts that the less closely related to native flora species are, the more likely they are to succeed as invaders, is tested here with an unprecedentedly thorough molecular phylogenetic approach, examining >100,000 phylogenies of the weed-rich thistle tribe Cardueae. Branch lengths between taxa were used as measures of evolutionary relatedness. Results show that invasive thistles are more closely related to natives than noninvasive introduced thistles, suggesting they share preadaptive traits with the natives that make them more likely to succeed as invaders.