Genetic relationships among and within populations of Phragmites australis (Cav.) Trin. ex Strudel in the Charles River watershed, MA, USA, were investigated using the Random Amplified Polymorphic DNA (RAPD) technique. Cluster analysis of resultant data grouped populations geographically with distance along the river, with one exception. It strongly separated the group of populations on the main stem of the river from those on a tributary, the Muddy River, suggesting a different sourer of propagules for these two population groups. Transects through large stands of Phragmites showed changes with distance in three out of four populations, indicating that stands consist of a few contiguous clonal individuals or of several individuals intermixed. Analysis of molecular variance assigned 1.71% of the variance in the data set to the component separating the groups of populations on the two rivers. The preponderance of variation resides among individuals within populations, implying that the populations are very closely related, and that variation in the metapopulation is small. This would suggest either that populations have been established primarily via vegetative propagules, or that the expansion of this plant's range rook place during a short time span. (C)2000 Elsevier Science B.V. All rights reserved.
