Genetic and morphometric insights into the Sardinian deciduous oaks (subgen. Quercus, sect. Quercus): taxonomy and conservation

Abstract This study examines the genetic and morphological variability within the Quercus pubescens s.l. complex of Sardinian white oak populations, including Q. congesta , Q. ichnusae , and Q. virgiliana . These tree taxa act as umbrella species in several climax communities across the Sardinia Island. A comparison of actual and potential cover of the different types of Sardinian deciduous oak forests was carried out. Ten EST-SSR markers were analysed to examine genetic diversity and differentiation within and among populations. Genetic structure was assessed using Bayesian clustering methods while relationships between populations were assessed by means of multivariate analyses. Five additional Q. pubescens populations from Italy, Spain, and Croatia and three populations belonging to Q. frainetto , Q. petraea , and Q. robur from peninsular Italy were also included in the genetic analyses. The morphometric analysis was performed on twelve leaf morphological traits focussing exclusively on the Sardinian populations. The results showed that deciduous oak forests occupy only a fraction of their potential area. Xero-thermic pubescent oak forests showed the greatest loss of their potential coverage. Neither genetic nor morphometric data revealed sufficient levels of diversity between populations to justify the current taxonomic classification of Sardinian pubescent oaks into four different taxa. Minimal genetic differentiation was found within the entire group of Q. pubescens s.l., whereas a clear separation among Q. frainetto , Q. petraea , Q. pubescens , and Q. robur was highlighted. Nevertheless, two major gene pools were identified within the Q. pubescens s.l. group with geographic distance among populations having a predominant influence over taxonomic boundaries.