The history of reed canarygrass in North America: persistence of natives among invading Eurasian populations.

Reed canarygrass (Phalaris arundinacea L.) is a major invader in North American wetlands that has also been planted as a forage crop for nearly a century. While the species is native to both North America and Eurasia, the geographic origin of invaders has remained unknown due to the previous inability to distinguish North American and Eurasian populations. The goals of this study were to (i) identify extant native North American populations if they exist, (ii) determine the geographic origin of present-day populations in North America, and (iii) compare the diversity among Eurasian and North American populations to determine whether there is evidence of a genetic bottleneck in North America. A total of 987 individuals from 373 accessions were investigated using 15 microsatellite markers. A subset of 37 individuals was sequenced at four chloroplast regions. The population structure of the species was inferred using Bayesian clustering approaches and a median joining tree. Native North American populations of reed canarygrass are still present in North America. However, only 3 of the 235 North American accessions sampled were of North American origin. All Eurasian subpopulations were present in North America and invading populations in North America were as diverse as populations in the Eurasian range. The Eurasian populations are far more common in North American wetlands today and suggest introduced Eurasian populations are more invasive than their North American counterparts although the mechanisms for the differences in invasibility remain a mystery.