Phylogeography of Quercus section Quercus Chloroplast DNA variation. Phylogeography of West Eurasian white oak plastome

Available knowledge on the European white oaks (Quercus, sect. Quercus) plastome still shows large gaps, mostly concerning the lack of a detailed phylogeny and information from southern Europe and adjacent Near East. We investigated DNA sequence polymorphism at two plastid loci on 270 individuals representing 12 white oak species/taxa and retrieved several hundred sequences from GenBank to fill this gap and contribute to a better comprehension of the white oak diversity and evolution. The modern European sect. Quercus species exhibit a little differentiated plastome, despite the current highly diversified taxonomy. In total, 29 haplotypes were identified, including two ancestral variants that are westerly and south easternly partitioned. The high- and low-frequency haplotypes also showed a well-structured geographical distribution consistent with the current phytogeographic framework of the European continent. The climatic and geological events that characterized the end of the Tertiary and Quaternary periods played a crucial role in triggering haplotype mixing, isolation, and in offering niche opportunities for more recent diversification. Euro-Mediterranean southern territories host a high and yet uncovered genetic variation; the role of the Italian peninsula as a crossroad and threshold for haplotype diversity in southern Europe clearly emerged.