[ Objective] This study was to analyze the two hydrochemical factors affecting the distribution of Ceratopteris thalictroides, further to provide basis for its habitat protection and population restoration. [ Method ] Twenty two hydrochemical parameters of 22 sampling sites in China＇s tropical and subtropical zones were respectively averaged for calculating their variation coefficients, of which the two showing significant differences were used for multiple comparisons and correlation analyses via least significant difference and correlation coefficient. E Result ] The correlation coefficients of all the 22 tested hydrochemical parameters varied hugely, but only pH value and conductivity showed significantly differences in two water body （type A and type B）. Analysis of correlation presented that pH value were positively correlated with conductivity; further the multiple comparisons showed that the significant difference of pH value was higher than that of conductivity. [Conclusion] With regard to the two hydrochemical parameters showing significant differences, pH value influences the distribution of C. thalictroides more.
The genetic variation in the critically endangered speciesIsoetes hypsophila was investigated using Random Amplified Polymorphism DNA (RAPD) markers. Thirteen primers were screened from sixty primers, and a total of 104 DNA fragments were scored, of which, 52 were polymorphic loci. Low-level genetic diversity within populations with PPB values ranging from 7.69%to 25.96%was found. An Anal ysis of Molecular Variance (AMOVA) indicated that the most of variance (78.30%) occurred between Yunnan and Si chuan. The variances among populations within regions and within populations were only 3.89%and 17.82%, respectively.
