Niche evolution in a northern temperate tree lineage: biogeographical legacies in cork oaks (Quercus section Cerris).

The article focuses on the evolutionary history, biogeography, and niche evolution of cork oaks (Quercus section Cerris) and their sister group, the holly oaks (Quercus section Ilex), in Eurasia. Using restriction site-associated DNA sequencing (RAD-seq) and a fossilized birth–death model calibrated with 47 fossils, the study reconstructs a dated phylogeny revealing an early Eocene divergence between East Asian and Western Eurasian cork oaks, followed by diversification into four Western Eurasian subsections during the Oligocene and Miocene. Ancestral niche reconstructions indicate that cork oaks originated in temperate, frost-free biomes at higher latitudes and later adapted to Mediterranean, arid, and continental climates, with leaf morphology evolving in correlation with these climatic shifts. The contrasting biogeographical histories of deciduous cork oaks and evergreen holly oaks, shaped by deep-time phylogenetic legacies, explain their present-day distributions and ecological diversity across Eurasia.