Nonnative M. vimineum has been expanding rapidly in the eastern United States, where it can negatively affect plant communities. Locally, the species is assumed to spread from roadsides into nearby forests, where it can form dense populations after disturbances, especially in light gaps. Using microsatellite markers, we quantified patterns of genetic variation and structure among populations at nine sites in West Virginia. We then examined patterns of local dispersal within each population, focusing on subpopulations along the roadside, those coalescing nearby along the forest edge, and subpopulations in the interior forest. We found that levels of genetic variation of M. vimineum were relatively low overall across populations but with genetic structure present among populations (Fst
= 0.60). Within populations, subpopulations along the roadside were genetically variable, containing 4 to 22 unique, multilocus genotypes. Many of these genotypes were also identified in the adjacent forest, consistent with local, diffusive spread from the roadway. However, several genotypes in the interior forest were unique to the population, indicating that dispersal from other sites may also occur. Overall, it appears that genetic diversity and structure in M. vimineum reflects a variety of processes, including localized dispersal and long-distance migration.