One genotype dominates a facultatively outcrossing plant invasion

Plant invasions are rarely homogenous. Processes such as selection, drift, gene flow, and founding events can rapidly shape the genetic diversity and spatial population structure of an invasion. We investigated the diversity, origins and population structure of Verbascum thapsus (common mullein), an introduced plant in North America. Despite this species being facultatively outcrossing, we found the invasion dominated by a single genotype (61% of plants were identical amplified fragment length polymorphism [AFLP] genotypes in the western USA). Fifty percent of the invasion populations were monotypic, and we found 32 genotypes overall in the 431 plants sampled from the invasion. In contrast, populations were much more diverse in the native Eurasian range, with 394 genotypes found in 479 plants. Further, we found an exact genetic match between the common genotype 1 in the USA and plants from Belgium and Germany. The identification of the most common and diverse invasive genotypes of common mullein allows their use in tests of management tools and further studies of mechanisms of this invasion.