Common reed, Phragmites australis (Cav.), is among the most widespread angiosperms in the world and is found on every continent except Antarctica. Phragmites grows in all aquatic and brackish environments and spreads through both asexual and sexual structures. In North America, an invasive, European genotype of common reed (Phragmites australis (Cav.) Trin. Ex. Steudel) is now abundant in habitats once colonized by native genotypes. Rapid expansion of populations in wetlands along the East Coast was previously thought to be driven by human disturbance, but evidence now suggests that a cryptic invasion of an European genotype has occurred in the eastern United States (and some western locations), and this biotype continues to spread across the continent.The native genotypes (P. australis subspecies americanus) can be distinguished from the exotic genotype based on morphological and genetic characteristics. Phragmites is represented by three distinct lineages in North America – native P. australis subsp. americanus, which is comprised of several dozen haplotypes, an invasive European haplotype, and P. australis subsp. berlanderi (commonly refered to as the Gulf Coast variety), which is of unknown origin.