Comparative systematics and phylogeography of Section in western Eurasia: inferences from plastid and nuclear DNA variation.

Oaks () comprise more than 400 species worldwide and centres of diversity for most sections lie in the Americas and East/Southeast Asia. The only exception is the Eurasian sect. that comprises about 15 species, most of which are confined to western Eurasia. This section has not been comprehensively studied using molecular tools. Here, we assess species diversity and provide a first comprehensive taxonomic and phylogeographic scheme of western Eurasian members of sect. using plastid () and nuclear (5S-IGS) DNA variation with a dense intra-specific and geographic sampling. Chloroplast haplotypes primarily reflected phylogeographic patterns originating from interspecific cytoplasmic gene flow within sect. and its sister section . We identified two widespread and ancestral haplotypes, and locally restricted derived variants. Signatures shared with Mediterranean species of sect. , but not with the East Asian oaks suggest that the western Eurasian lineage came into contact with only after the first (early Oligocene) members of sect. in Northeast Asia had begun to radiate and move westwards. Nuclear 5S-IGS diversification patterns were more useful for establishing a molecular-taxonomic framework and to reveal hybridization and reticulation. Four main evolutionary lineages were identified. The first lineage is comprised of , and and appears to be closest to the root of sect. . These taxa are morphologically most similar to the East Asian species of , and to both Oligocene and Miocene fossils of East Asia and Miocene fossils of western Eurasia. The second lineage is mainly composed of the widespread and the narrow endemic species , and . The third lineage comprises three Near East species (, and ), well adapted to continental climates with cold winters. The forth lineage appears to be the most derived and comprises and . and displayed high levels of variation; and previously treated as subspecies of and likely deserve independent species status. A trend towards inter-specific crosses was detected in several taxa; however, we found no clear evidence of a hybrid origin of . and , as currently assumed.