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Quercus petraea (sessile oak) has a scattered distribution in southern and central Italy. The objective of this work was to evaluate the level and distribution of diversity in five Italian populations of Q. petraea by using morphological markers and hypervariable molecular markers such as microsatellites. Forty-eight morphological traits and six nuclear and three plastid loci were scored for each population. Evidence for differentiation in both sets of traits was found, but patterns of differentiation of morphological traits did not coincide with microsatellite differentiation. Morphological variation was correlated with ecological conditions at the site of origin. Analysis of molecular variance revealed significant genetic variation among populations (P < 0.001), both at the nuclear and plastid levels. There was a slight, but significant, correlation between nuclear genetic distance and geographic distance. The relatively high genetic diversity in the populations analysed indicates that the maintenance of their evolutionary potential is possible if population sizes are maintained or increased. Low levels of haplotype diversity found within the small southernmost population (Piano Costantino) indicates that genetic erosion may increase the extinction risk for this population.

Variation in leaf morphology of Quercus petraea in response to several ecological conditions has been studied extensively, although not explicitly in the context of within-and among-tree variation. This study examined leaf morphology and anatomy of Q. petraea, growing in five natural Italian populations adapted to different ecological environments, to understand the pattern of within-and among-tree variation in this species. We used an ANOVA model with both crossed and nested effects. All levels contributed significant components of variation. Within-tree variation due to branch position was large, particularly in thickness and productivity (40%). For 19 of 32 variables, the variation among trees was surprisingly lower than the within-tree variation explained by branch position. Trends in leaf morphology and anatomy with branch position exhibited the sunshade dichotomy. Patterns of crown plasticity showed lower values in the two xeric populations. Results suggest the need for taxonomic studies to consider variation as a quantitative attribute of individual trees.

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