During invasive plant arrival and spread, changes occur to cause genetic variation in the invasive plant populations. These changes can be used to find the degree of relatedness among populations and to track the path of spread on invasive plants. One such invasive plant in the eastern United States is Japanese Knotweed (Polygonum cuspidatum) which forms dense clusters that shade out native plants. Knotweed is currently invading Southeast Ohio and makes an excellent model for tracing the path of invasion. The purpose of this study was to trace the path of invasion for Japanese Knotweed in the eastern United States by studying its genetic variation. Genetic diversity has been compared among populations and among regions by studying 1) genetic and 2) phenotypic variation to determine the path of spread and whether multiple introductions have occurred in the eastern United States.

Results/Conclusions

We have found phenotypic variation in populations of Japanese Knotweed. Variation exists in leaf length and leaf base width, in shoot height, and in shoot diameter. We found genetic variation from three microsatellite DNA marker regions among three regions (Michigan, Southeast Ohio, and the southern Appalachian region of Tennessee and North Carolina). The variation found suggests that the populations studied in the three regions are differentiated from one another due to multiple founding events or from genetic drift. This data can be used to plan various methods of control and management of this species.