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Genetic characterization of Cycas panzhihuaensis (Cycadaceae): crisis lurks behind a seemingly bright prospect


 Background
 
 Cycas panzhihuaensis L. Zhou & S. Y. Yang (Cycadaceae) is an endangered gymnosperm species endemic in the dry-hot valley of Jinsha River basin from southwest China. Although the wild C. panzhihuaensis population from Panzhihua Cycad Natural Reserve is well protected, other known populations that fall outside the natural reserve may preserve specific genetic resources while face with larger extinction risk because of lacking essential monitoring.
 
 Methods
 
 In this study, we analyzed the genetic diversity, phylogeographical structure and demographic history of C. panzhihuaensis from seven known locations so far by sequencing three chloroplastic DNA regions (psbA-trnH, psbM-trnD, and trnS-trnG), four single-copy nuclear genes (PHYP, AC5, HSP70, and AAT) from 61 individuals, and eleven microsatellite loci (SSR) from 102 individuals.
 
 Results and Discussion
 
 We found relative high genetic diversity within populations and high genetic differentiation among the populations of C. panzhihuaensis, which is similar with the other Asian inland cycads. Despite no significant phylogeographical structure was detected, small and unprotected populations possess higher genetic diversity and more unique haplotypes, which deserve due attention. Results of demographic dynamics suggest that human activity is the key factor that leads C. panzhihuaensis to endangered status. Basing on the genetic characterization of C. panzhihuaensis, we proposed several practical guidelines for the conservation of this species, especially for its small populations.