Genetic variation among and within populations of Phragmites australis in the Charles River watershed

Genetic relationships among and within populations of Phragmites australis (Cav.) Trin. ex Strudel in the Charles River watershed, MA, USA, were inves tigated using the Random Amplified Polymorphic DNA (RAPD) technique. Cluste r analysis of resultant data grouped populations geographically with distan ce 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 Mu ddy River, suggesting a different sourer of propagules for these two popula tion groups. Transects through large stands of Phragmites showed changes wi th distance in three out of four populations, indicating that stands consis t of a few contiguous clonal individuals or of several individuals intermix ed. Analysis of molecular variance assigned 1.71% of the variance in the data s et to the component separating the groups of populations on the two rivers. The preponderance of variation resides among individuals within population s, implying that the populations are very closely related, and that variati on in the metapopulation is small. This would suggest either that populatio ns have been established primarily via vegetative propagules, or that the e xpansion of this plant's range rook place during a short time span. (C)2000 Elsevier Science B.V. All rights reserved.