Phylogeographic studies of plants in China: Advances in the past and directions in the future

Phylogeography has been one major focus of evolutionary biology in recent years, with many important advances in Chinese species. In this issue, we collected 11 phylogeographic studies of plants by Chinese laboratories. We further synthesized the main findings and patterns emerging from these and previous phylogeographic studies in China and asked where phylogeographic research should be directed in the coming years. Numerous examples have shown that phylogeographic patterns in China did not show an expected expansioncontraction pattern at large scale, mirroring the geological records showing that no unified ice sheet had developed in China during the Quaternary Period. Instead, regional expansions and intraspecific divergences are very common in most studied species during the Quaternary oscillations. Different intraspecific lineages or alleles (haplotypes) were detected in multiple localized refugia, from where regional or local expansions are likely to have started. Hybridizations and introgressions are frequent between intraspecific lineages or between different species. We also reviewed computational methods for phylogeographic analyses. Despite the great progress made in recent years, there remains much to discover about the spatialtemporal dimensions and underlying speciation mechanisms of Chinese plants. Phylogeographic studies represent a key knot that connects the genus phylogeny (macroevolution) and speciation and adaptation (microevolution). Therefore, we advocate that: (i) phylogeographic studies of plants in China should be directed to the closely related species or a monophyletic group (for example, a genus or a section) in the coming years; and (ii) population genetic data based on direct sequencing multiple loci, especially those from nuclear genome and statistical tests should be widely adopted and enforced. The recovered intraspecific divergences and phylogeographic patterns of multiple-species may allow us to better understand the high plant diversity in China and set up concrete hypotheses for studying plant speciation and diversification mechanisms in this region.