In this study

twenty-four present locations of Ceratopteris thalictroides populations and twenty-two locations where the species had been previously recorded but is now extinct were investigated in China.These sites of the extinct populations currently have higher water pH and conductivity values than the current sites of remaining populations.The results indicate that the geographic distribution and occurrence of C.thalictroides were associated with the destruction and loss of aquatic habitats.The genetic diversity within and among thirteen populations of C.thalictroides was investigated using ISSR markers.The percentage of polymorphic bands（PPB） was 65.19%.Analysis of Molecular Variance（AMOVA） showed that 33.91% of variability was partitioned among populations.The results indicate C.thalictroides possesses an intermediate level of genetic diversity at species level and lower genetic differentiation between populations.High gene flow via spore dispersal in an earlier period when C.thalictroides was widely distributed in China is a plausible reason for the low genetic differentiation among populations.