Identification of High-Impact Anatomical Markers in Verbascum Genetic Resources: An Integrative Study of Section Bothrospermae from a Major Biodiversity Corridor

This study evaluated the taxonomic significance of the anatomical and micromorphological characteristics of the Verbascum genus (Scrophulariaceae) using a comprehensive quantitative approach. This study focused on 20 Verbascum taxa that naturally occur in the northwestern part of Anatolia, a region where the Euro-Siberian, Irano-Turanian, and Mediterranean phytogeographic zones converge. Precise anatomical measurements and multivariate statistical techniques were used. Specimens were collected during the flowering stage. Cross-sections of stems and leaves were analyzed using light microscopy, and scanning electron microscopy (SEM) was used to examine the micromorphology of the leaf surfaces. Quantitative anatomical data were collected using ImageJ and analyzed using Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA). PCA revealed that certain quantitative anatomical features, particularly the dimensions of the lower epidermal cells and collenchyma cells of the leaves, were most effective in differentiating the taxa, with pubescence-related characteristics providing additional qualitative insights into their taxonomy. HCA produced distinct clusters that largely corresponded with established species boundaries and clearly demonstrated intraspecific variations. These results highlight the importance of quantitative anatomical traits in distinguishing species and subspecies within Verbascum and emphasize the need for controlled regional sampling to address taxonomically complex plant groups.