Darwin's naturalization hypothesis challenged

Naturalized plants can have a significant ecological and economic impact1, yet they comprise only a fraction of the plant species introduced into new areas by humans2. Darwin proposed3 that introduced plant species will be less likely to establish a self-sustaining wild population in places with congeneric native species because the introduced plants have to compete with their close native relatives, or are more likely to be attacked by native herbivores or pathogens4,5, a theory known as Darwin's naturalization hypothesis6. Here we analyse a complete list of seed-plant species that have been introduced to New Zealand and find that those with congeneric relatives are significantly more, not less, likely to naturalize — perhaps because they share with their native relatives traits that pre-adapt them to their new environment.