Pleistocene glaciation advances the younger temporal dimension of species diversification in a major biodiversity hotspot

O_LIThe expansive Himalayan-Hengduan Mountains (HM) and Qinghai-Tibet Plateau (QTP) form a biodiversity hotspot imperiled by global change. The species diversity, resulting from myriad factors led to plant diversification from 10 million years ago till now. However, despite understanding speciation timing better, a lack of in-depth population-level studies and a dearth of organismal sampling among closely related species and populations leaves an incomplete view of diversification trends and biotic influences. C_LIO_LIWe delve into the complex factors influencing diversification through genomic and eco-morphological analysis within the Stellera chamaejasme L. complex, known for its significant floral diversity. C_LIO_LIOur results uncover four cryptic species, indicating a more recent and younger diversification period ([~]2.67-0.9 Mya), driven by Pleistocene glaciation and a complex set of interacting biotic factors. These factors prompted allopatric speciation and advocated cyclical warming-cooling episodes along latitudinal and altitudinal gradients throughout the Pleistocene. C_LIO_LIThe study emphasizes the existence of cryptic species within these mountains, broadening our understanding of species diversification to more recent than previously recognized. This novel perspective may reshape evolutionary paradigms in plant science. Additionally, it also brings to light concerns over future warmings possible impacts on alpine species distribution and speciation, underlining the urgency for increased conservation efforts. C_LI