Understanding the mechanisms underlying spatial mismatches between species richness and diversification rates remains a central challenge in macroecology. Here, we investigate how historical environmental regimes and intrinsic traits jointly shape biodiversity gradients in Chinese Clematis. We integrated a time-calibrated phylogeny of 169 species with extensive distribution records and functional morphological traits, and applied diversification analyses, ancestral reconstructions, and structural equation modelling (SEM) to disentangle the relative contributions of historical climate, contemporary environment, and trait variation. We reveal a pronounced geographic mismatch: species richness peaks in the humid southeast, whereas diversification rates are highest in the arid northwest. This pattern is associated with an early diversification burst (ca. 8.5–7.5 Ma) and subsequent northwestward expansion (ca. 5.5 Ma), linked to Late Miocene climatic dynamics. Adaptive traits promote diversification under harsh conditions, while environmental filtering and limited evolutionary time constrain lineage accumulation. Our results demonstrate that spatial biodiversity gradients emerge from the joint effects of environmental history and trait-mediated responses, leading to a decoupling of species richness and diversification. These findings highlight the importance of integrating macroevolutionary dynamics and ecological processes to understand the spatial structuring of biodiversity.