Ancient alleles drive contemporary climate adaptation in an alpine plant

Adaptive evolution is key for species to persist in a warming climate. However, how adaptive genetic variants arise and shape both past and future evolutionary trajectories remains largely unknown. In this work, we integrate genomics with functional and ecological assays to unravel the evolutionary history and adaptive potential of alleles governing adaptation to climate through flowering time in an Alpine carnation. We reveal that “warm” and “cold” alleles of the flowering inhibitor CENTRORADIALIS (DsCEN/2) originated through recombination of highly divergent haplotypes during the carnation radiation, implicating ancestral variation in seeding climate-adaptive alleles. These alleles survived in glacial refugia before mediating the species’ range expansion in response to postglacial warming. We predict that, by recapitulating past evolution, warm alleles will continue to facilitate adaptation under future climate change.