Genotyping-by-Sequencing Reveals Low Genetic Diversity and Pronounced Geographic Structuring in the Endangered Medicinal Plant Coptis chinensis var. brevisepala

<i>Coptis chinensis</i> var. <i>brevisepala</i> W. T. Wang & P. G. Xiao is an endemic and endangered medicinal plant in China whose wild populations are rapidly declining under the combined pressures of overharvesting, climate change, and habitat fragmentation. Using genotyping-by-sequencing, we analyzed 87 individuals from 15 populations in Zhejiang Province, China, and identified 155,611 high-quality SNPs. The species exhibited low genetic diversity and strong genetic differentiation among populations with restricted gene flow (population-averaged <i>H</i>_o = 0.066, <i>H</i>_e = 0.067, <i>π</i> = 0.078, <i>F</i>_IS = 0.029, <i>F</i>_ST = 0.503, <i>N</i>m = 0.329, gRelMig = 0.136). Analysis of molecular variance showed that variation among populations accounted for 73.58% of the total genetic variation (<i>p</i> < 0.001). A phylogenetic tree, principal component analysis (PCA), and admixture analysis consistently resolved the 15 populations into two major groups, which could be further subdivided into four subgroups. Mantel and partial Mantel tests indicated that geographic isolation is the primary driver of genetic differentiation, while environmental factors such as ultraviolet radiation and low temperature may contribute to fine-scale divergence at local spatial scales. Furthermore, MMRR analysis provided further confirmation of the independent and dominant role of geographic isolation. This study provides key data on the genetic diversity and population structure of <i>C. chinensis</i> var. <i>brevisepala</i> and offers a genetic basis for developing regionally differentiated conservation strategies and promoting its sustainable utilization.