Phylogeny and biogeography of Impatiens sect. Racemosae (Balsaminaceae) based on nrDNA and plastome sequences, emphasizing diversification in the Himalaya and the Hengduan Mountains

Abstract Elucidating the mechanisms driving evolutionary radiation remains a crucial yet challenging endeavor, particularly regarding the evolutionary processes of taxa within key biodiversity areas. In this study, we investigated factors associated with orogenesis and climate cooling that influenced the evolutionary radiation of Impatiens sect. Racemosae (Balsaminaceae) in the Himalaya, Hengduan Mountains (HDM), and surrounding areas. We constructed a robust phylogenetic framework for the section based on plastomes and nuclear ribosomal DNA (nrDNA) with expanded taxon sampling. In addition, we estimated divergence times and ancestral ranges, and conducted diversification rate analyses, ancestral niche reconstruction, and ecological niche modeling for the section. Our findings revealed four major clades within the section, each well supported with high bootstrap values. We inferred that the section originated in the Himalaya during the late Miocene and experienced in situ diversification around 8.74 Ma. Subsequently, dispersal occurred from the Himalaya into surrounding regions through multiple events. Notably, during the middle Pliocene (4.1 Ma), species migrated into the HDM, underwent further in situ diversification, and several lineages subsequently dispersed into the Yunnan‐Guizhou Plateau and Southeast China, which is consistent with the timing of the HDM orogenesis. The species richness distribution pattern of I. sect. Racemosae was strongly influenced by precipitation, and species within the section exhibited high levels of niche conservatism. Ecological niche modeling revealed a notable pattern of contraction, extension, and subsequent contraction in the distribution of the section after the middle Pliocene. Our findings demonstrate that the evolutionary radiation of I. sect. Racemosae was shaped by the cumulative effects of the HDM orogenesis, Central Asia aridification, and global climate cooling. The elucidation of these key factors provides insights into the dispersal and diversification patterns of I. sect. Racemosae within a key biodiversity area, thereby advancing our understanding of the mechanisms underlying its evolutionary radiation in this region.