Origin of non-native Phragmites australis in North America, a common wetland invader

Molecular genetic data are often used to identify the provenance of invasive species in order to gain insight into processes such as founder effects that are associated with novel introductions. In addition, origins must be determined before natural herbivores or predators can be identified as potential agents of biological control. In North America, an increasingly problematic invader of wetlands is a Eurasian lineage of the common reed, Phragmites australis. Although thought to have been introduced from Europe in the 19(th) century, a more specific geographical source has not yet been identified. In this study, we compared the genotypes of North American invasive P. australis with genotypes collected from the United Kingdom and continental Europe. Our data identify the United Kingdom as the most likely origin of invasive P. australis. In addition, by comparing the genetic diversity of invasive P. australis with plants from its native land, and also with North American native P. australis, we show that despite a founder effect the genetic diversity of the introduced stands remains relatively high, whereas the genetic diversity of native stands in Canada is low. Collectively, these findings could have important implications for the future biodiversity of wetlands in North America because adaptation to environmental change is most likely in populations and species with relatively high genetic diversity.