摘要The evolution of the latitudinal diversity gra-dient(LDG),characterized by a peak in diver-sity toward the tropics,has captured significant attention in evolutionary biology and ecology.However,the inverse LDG(i-LDG)mechanism,wherein species richness increases toward the poles,remains inadequately explored.Cy-cads are among one of the oldest lineages of extant seed plants and have undergone ex-tensive diversification in the tropics.Intrigu-ingly,the extant cycad abundance exhibits an i-LDG pattern,and the underlying causes for this phenomenon remain largely elusive.Here,using 1,843 nuclear genes from a nearly com-plete sampling,we conducted comprehensive phylogenomic analyses to establish a robust species-level phylogeny for Cycas,the largest genus within cycads.We then reconstructed the spatial-temporal dynamics and integra-ted global environmental data to evaluate the roles of species ages,diversification rates,contemporary environment,and conserva-tism to ancestral niches in shaping the i-LDG pattern.We found Cycas experienced de-creased diversification rates,coupled with the cooling temperature since its origin in the Eocene from continental Asia.Different regions have distinctively contributed to the forma-tion of i-LDG for Cycas,with the northern hemisphere acting as evolutionary museums and the southern hemisphere serving as cra-dles.Moreover,water-related climate variables,specifically precipitation seasonality and po-tential evapotranspiration,were identified as paramount factors constraining Cycas species richness in the rainforest biome near the equator.Notably,the adherence to ancestral monsoonal climates emerges as a critical factor in sustaining the diversity pattern.This study underscores the imperative of integrating both evolutionary and ecological approaches to comprehensively unravel the mechanisms un-derpinning global biodiversity patterns.