Origin of non-native Phragmites australis in North America, a common wetland invader Kaloni Plut 1 , Jennifer Paul 2 , Claudia Ciotir 2 , Meghan Major 1 and Joanna R. Freeland 3, * With 2 figures and 2 tables Abstract: 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 identiied 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 speciic geographical source has not yet been identiied. In this study, we compared the genotypes of North American inva- sive 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 ge- netic diversity of native stands in Canada is low. Collectively, these indings 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. Key words: Phragmites australis, genetic diversity, invasive species, wetlands, biological control, founder effect. Authors’ addresses: 1 Forensic Science Program, Trent University, Peterborough, Ontario, Canada K9 J 7B8. 2 Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, Canada K9 J 7B8. 3 Department of Biology, Trent University, Peterborough, Ontario, Canada K9 J 7B8. * Corresponding author; joannafreeland@trentu.ca Fundam. Appl. Limnol. Vol. 179/2, 121–129 Article Stuttgart, May 2011 © 2011 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/1863-9135/2011/0179-0121 1863-9135/11/0179-0121 $ 2.25 Introduction Although invasive species continue to cause remark- able levels of environmental change (Pimentel et al. 2005, Vila et al. 2010), and have therefore been the focus of a large and growing number of studies, it re- mains unclear what processes enable a few introduced species to become successful invaders while the ma- jority either perish or maintain very restricted distribu- tions (Kanarek & Webb 2010, and references therein). This uncertainty may partly explain why the manage- ment of established invasive species is challenging and seldom successful: although several strategies ex- ist for controlling and eradicating invaders, including chemical, biological, mechanical, and manual control, these often result in only short-term eradication, and sometimes entail detrimental non-target effects (DiTo- maso 2000, Blossey 2003, Olson & Roy 2008, Tewks- bury et al. 2002). Identifying the source population of an invasive species may help us to understand some of the processes that drive invasions, for example by enabling comparisons of genetic diversity or niche oc- cupancy between native and invaded habitat (Cheang et al. 2010, Mandle et al. 2010, Dawson et al. 2011). In addition, biological control of an invasive species requires knowledge of its geographical origin before