Abstract: The genetic diversity of Bryum argenteum Hedw. was studied based on 252 samples from 11 inland and 32 island populations using Inter-Simple Sequence Repeat (ISSR) markers. Significant genetic differentiation between island and inland populations was detected, with a higher degree of differentiation found in the island populations (G_st=0.453) compared with the continental populations (G_st=0.387). There was a significant correlation between genetic differentiation of the tested samples and their geographical origin (r=0.478, n=175, P<0.001), indicating a significant effect of geographical isolation on genetic differentiation among the populations of mosses. Genetic variation among the island populations of B. argenteum was low, varying from 29.4% to 29.7% among populations. 43 populations were divided into 10 groups based on the ISSR results using cluster analysis. Both geographic origin and environmental heterogeneity exerted marked effects on the genetic diversity of B. argenteum. The spread of propagules was likely impacted by watershed isolation to a certain degree.