Legacies of Past Climate Change Shape Future Resilience of Typha latifolia at Its Rear Edge in East Asia.

Global warming poses a significant threat to rear-edge populations owing to their geographically marginal distributions. Understanding the historical dynamics and future trajectories of these populations is crucial for developing effective conservation strategies, yet they remain poorly understood. Here, we employed landscape genomic approaches on 153 samples from 24 Typha latifolia populations spanning its fragmented rear edge in East Asia, to explore demographic history, local adaptation, climate vulnerability and resilience potential. Our analyses reveal that repeated Pleistocene climatic cycles of drastic cooling and warming shaped five genetically distinct and geographically fragmented groups. Long-term persistence through phases of expansion and climate-driven fragmentation has enabled each group to evolve unique local adaptation strategies tailored to their specific environmental conditions. Despite current fragmentation, most populations exhibit low genomic offset and risk under future climate scenarios, suggesting retained adaptive capacity. Nonetheless, we identify maladaptation hotspots in Northeast China associated with no-analog climate conditions, pointing to localized vulnerability. These findings highlight how ancient climatic legacies have shaped genomic adaptations that mitigate climate risk, positioning rear-edge populations as critical reservoirs of resilience under accelerating global change. Preserving these unique lineages and maintaining habitat connectivity will be essential to safeguard their evolutionary potential in the face of ongoing environmental challenges.