Phylogeography of Achyranthes bidentata (Amaranthaceae) in China's Warm-Temperate Zone Inferred from Chloroplast and Nuclear DNA: Insights into Population Dynamics in Response to Climate Change During the Pleistocene

Previous phylogeographic studies of the warm-temperate zone in China focused on woody plants, but little attention was given to the climate-sensitive herbaceous plants. In this work, we implemented a phylogeographic survey on the perennial herb Achyranthes bidentata in China's warm-temperate zone. The sequence variation of cpDNA and nDNA was examined across 209 individuals from 21 populations. A total of 11 chlorotypes and 26 ribotypes were identified. The cpDNA data showed weak population genetic differentiation and could not divide the 21 populations into different genetic groups. By contrast, the nDNA data revealed stronger genetic differentiation than cpDNA and could divide these populations into two genetic groups. The cpDNA and nDNA data both gave unambiguous signs of recent sudden population expansion. Based on the cpDNA and nDNA data, the estimated time of population expansion occurred at interglacial Marine Isotope Stage (MIS) 9 of the Penultimate Glaciation in China. The cpDNA and nDNA data suggested that the glaciation during this period deeply influenced the current distribution patterns and intraspecific divergence of A. bidentata. Our survey showed that A. bidentata tracked climatic oscillations by a large range of southward retreat into three main refugia during MIS 8, followed by the sudden northward expansion from these refugia during MIS 9.