The ‘Tanaka‐Kaiyong Line’ ( TKL ) is a major phytogeographic boundary in Southwest China, separating East Asia's Sino‐Himalayan and Sino‐Japanese Floras. However, little is known about the importance of this boundary in promoting intraspecific phylogeographic subdivision and divergence. Using chloroplast (cp DNA ) and nuclear‐intron ( nDNA ) sequence data, we reconstructed the population history of Sophora davidii , a drought‐...