Cengiz Yucedag, Ebru Kilic Karaman, Oliver Gailing
Leaf shape differentiation between Quercus vulcanica and Q. frainetto using geometric morphometrics
Dendrobiology 2026, vol. 95: 66-76
https://doi.org/10.12657/denbio.095.005
Abstract:
Quercus vulcanica Boiss. & Heldr. ex Kotschy and Q. frainetto Ten. are closely related oak species with little genetic differentiation and slight morphological differences in Türkiye possibly as result of hybridization and phenotypic plasticity. While leaf morphology offers strong phenotypic cues for quantitative studies, traditional morphometrics frequently fails to capture these fine-scale differences. The objective of this study is to use geometric morphometrics to measure symmetric and asymmetric leaf shape variation using allometric effects and determine how population-level morphological differentiation, putative hybridization and altitude affect the interspecific differentiation between these two species. A total of 222 leaves from four Q. vulcanica and two Q. frainetto populations in Türkiye were digitized at 13 homologous landmarks to capture bilateral leaf geometry, enabling the analysis of symmetric and asymmetric shape variation. Generalized Procrustes Analysis, PCA, discriminant analysis and allometric and correlation assessments were performed in MorphoJ and SPSS to evaluate interspecific differences, population-level variation and associations with diameter at breast height and altitude. These analyses revealed that interspecific differentiation between Q. vulcanica and Q. frainetto is primarily associated with symmetric leaf shape components, particularly lamina width, lobe expansion, and petiole morphology, whereas asymmetric variation showed extensive overlap and lacked taxonomic relevance. 2B-PLS analyses indicated a weak to moderate association between leaf size and symmetric shape variation, especially in Q. vulcanica, while asymmetric shape variation was largely independent of size. Population-level comparisons showed clear morphological differentiation with low putative hybridization (2.9–12.2%) based on morphometric intermediacy criteria, and correlations with tree diameter highlighted size-dependent shape changes in Q. vulcanica, whereas altitude had little influence on leaf morphology in either species. It will be crucial to conduct future studies that integrate geometric morphometrics with genomic, eco-physiological and experimental methods over wider environmental gradients. Such integrative research will clarify the relative contributions of plasticity, adaptability and developmental constraint to the evolution of oak leaf shapes.
Keywords: hybridization, population-level morphology, oak taxonomy, allometry