Leaf Shape and Size Differentiation in White Oaks: Assessment of Allometric Relationships among Three Sympatric Species and Their Hybrids

A combined genetic and morphometric approach was used to study leaf shape and size variability among three sympatric and interfertile white oak species (Quercus frainetto, Quercus petraea, and Quercus pubescens) sampled in a mixed forest in central Italy. Leaf shape and size were analyzed separately to discriminate species, to identify unique leaf shape traits, and to analyze the relationships between hybrid phenotypes and their parental species. In addition, the covariation of leaf shape and size (i.e., allometry) was tested at the intraspecific level, and the differences in allometric trajectories were compared among species and hybrids. Finally, size correction of leaf shape data allowed quantification of the contribution of allometry to total variability and testing of its effect on species differentiation. Within pure oak species, leaf allometry was a significant component of leaf variation related to environmental variability, while when hybridization occurred leaf allometry was affected by the inheritability of both shape and size leaf traits. This study highlights the role of size and shape leaf covariation in the evolutionary processes of white oaks.