Tetracentron sinense (Trochodendraceae) is an Arcto-Tertiary relict with rich fossil records and a relatively broad extant geographical distribution that extends further south than the other Arcto-Tertiary relicts. T. sinense provides an excellent opportunity to further explore the effects of late Cenozoic climate change in the East Asian temperate and subtropical floras. 

 In order to evaluate whether and how Pleistocene and pre-Pleistocene climate changes helped to influence current phylogeographical patterns, and to describe the current patterns of genetic diversity and their implications for conservation, PhD student SUN Yanxia, under the supervision of Prof. LI Jianqiang and Prof. WANG Hengchang from Wuhan Botanical Garden, conducted phylogeographical analyses of 157 T. sinense  individuals from 27 populations in southwestern and central subtropical China using four chloroplast DNA intergenic spacer regions.  

Results revealed that three of the 21 recovered haplotypes were widely distributed, but most were restricted to particular regions. Populations with high haplotype diversity were located in western Hubei, southern Sichuan and southern Chongqing. The two earliest-diverging haplotypes were found in southwestern China. The haplotype distribution of T. sinense demonstrated significant phylogeographical structure. 

The extant distribution of T. sinense was likely to have been shaped by both pre-Quaternary and Pleistocene climate changes. Southwestern China may have served as an important refugium for T. sinense throughout the Neogene, while the species also occupied multiple refugia during the late Pleistocene glacial periods. Populations of T. sinense were resolved into five allopatric groups, between which there is apparently no seed movement. 

This research suggested that efforts should be made to protect populations in southwestern regions in order to preserve as much of the ancient genetic diversity of this phylogenetically distinctive and increasingly threatened species. 

Results entitled “Chloroplast phylogeography of the East Asian Arcto-Tertiary relict Tetracentron sinense (Trochodendraceae)” were published in Jornal of Biogeography. This work was founded by the Knowledge Innovation Project of the Chinese Academy of Sciences and by grants from the National Natural Science Foundation of China. 

The distribution of 21 cpDNA haplotypes and five SAMOVA-derived groups identified within 27 Tetracentron sinense populations from southwestern and central subtropical China (Image by SUN Yanxia)