Investigating the Discriminative Power of Anatomy and Micromorphology in Verbascum Taxonomy: A Detailed Statistical Analysis

This study evaluates the taxonomic significance of anatomical and micromorphological characters in the genus Verbascum (Scrophulariaceae) using a comprehensive and quantitative approach. Twenty Verbascum taxa naturally distributed in the Istanbul region, which is part of the genus's diversity center, were examined using detailed anatomical measurements and multivariate statistical analyses. Fieldworks were conducted between 2021 and 2024 with specimens collected during the flowering stage. Stem and leaf cross-sections were analyzed by light microscopy, and leaf surface micromorphology was examined using scanning electron microscopy (SEM). Quantitative anatomical data were obtained using ImageJ and evaluated using Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA). PCA revealed that a limited number of quantitative anatomical features had the highest discriminative power among the taxa studied; particularly leaf lower epidermal cell size and stem colenchyma cell size, while characters related to pubescence provided complementary qualitative support. HCA produced well-resolved clusters that largely corresponded to known species boundaries and also clearly demonstrated intraspecific differentiation. Overall, these results highlight the value of quantitative anatomical characters for species and subspecies delimitation within Verbascum and reveal the importance of controlled regional sampling in resolving taxonomically complex plant groups.