5 Conclusion
In conclusion, our study on the genetic diversity and structure ofNotholirion sheds light on the intricate evolutionary history and adaptive mechanisms of this genus. The observed high genetic diversity of Notholirion , surpassing the average of angiosperms, is attributed to ITS early divergence in the late Oligocene andITS adaptation to diverse climatic and geological events duringITS evolution. The unique ”sky island” environments, resulting from complex topography in the Himalayan-Hengduan Mountains, contribute to the isolation of populations and, consequently, high genetic differentiation. The AMOVA analyses revealed substantial genetic variation among Notholirion populations, indicating limited communication between populations due to specific habitat requirements, restricted seed dispersal, and environmental factors influencing gene flow. This genetic differentiation is consistent with the impact of complex geological activities and climate changes in the Himalayan-Hengduan Mountains region. Phylogenetic analysis confirmed the monophyletic nature of Notholirion , with N. thomsonianumidentified as the earliest divergent taxon. However, incongruences between nuclear and chloroplast gene trees suggest the influence of incomplete lineage sorting and hybridization, common phenomena in plant phylogenetics. The origin and diversification of Notholirion are closely tied to the uplift events on the Tibetan Plateau. The late Miocene and Pleistocene periods played pivotal roles in the evolution and distribution of Notholirion species, with significant climate fluctuations contributing to species divergence. The Last Glacial Maximum, in particular, led to the formation of distinct species, emphasizing the impact of Quaternary Ice Age climate changes on plant ranges and population dynamics. Our findings propose thatNotholirion , as a high-altitude taxon, survived the ice age through persistence in multiple refugia, particularly in the Hengduan Mountains region. The study challenges previous assumptions about the uniformity of ice cap coverage in the Tibetan Plateau and Hengduan Mountains during the Quaternary period, suggesting a more nuanced response of cold-tolerant plant taxa to climate changes. Overall, this research contributes valuable insights into the evolutionary and ecological dynamics of Notholirion , highlighting the importance of considering multiple factors, including geological events, climatic changes, and specific ecological, in understanding the genetic diversity and adaptive strategies of high-altitude plant taxa.