Leaf shape variation and differentiation in three sympatric white oak species revealed by elliptic Fourier analysis

In this paper, elliptical Fourier descriptors (EFDs) were used to study leaf shape variability as a “size-free” attribute of three sympatric and inter-fertile white oak species (Quercus frainetto, Q. petraea and Q. pubescens) sampled in a forest located in central Italy. Symmetric and asymmetric leaf components were analysed by multi-variate analysis of variance (MANOVA) and canonical variate analysis (CVA), separately, with the result that significant differences between the species were explained by symmetric leaf shape traits, whereas asymmetric components did not distinguish between the oak species. Correlation analyses found that the relationships between geographical location, environmental factors and leaf shape were not significant for the three pure species, while a significant correlation was found for the unclassified trees (putative hybrids), suggesting that leaf shape traits, analysed as a symmetric characteristic and without size effects, are indicative of specific genotypes and can be used to describe and explore morphological patterns, which are themselves indicative of hybridization and introgression in white oak species. Elliptic Fourier analysis (EFA) appears to be particularly useful for analysing leaf shape variability and discrimination in the subgenus Quercus, providing an important tool for visualizing the shape attributes that characterize this species complex and playing a notable role in the identification and systematics of this plant subgenus.