Anatomical, micromorphological and karyological contributions to the Periploca graeca (Apocynaceae) taxon

Periploca graeca L. (Garipler urganı) is currently treated as a species-level taxon without any infraspecific taxa in modern classifications. In this study, comprehensive stem and leaf anatomy and micromorphology, and somatic chromosome number of P. graeca taxa, collected from different populations in Türkiye, were examined comparatively, for the first time, using light microscopy and Scanning Electron Microscopy (SEM). In anatomical examinations, stems contained numerous groups of small, thick-walled cortical sclerenchymatic fibers; bifacial and hypostomatic leaves included anomocytic and parasitic stomata; and bicollateral vascular bundles, druse crystals, and laticifers were found throughout stems and leaves. In SEM examinations, stems were glabrous, petiole and lamina surfaces were covered with densely villous indumenta, or relatively glabrous, and epicuticular wax layer was rough on the stem and petiole, and radially striated on the leaf blade. Non-articulated laticifers, located throughout the midrib, petiole and stem, and “colleters”, known as glandular hairs located at the base of the petiole (defined as the standard type), were determined as the two main glandular structures. The somatic chromosome number was determined as 2n = 22 for the both populations. Parametric and non-parametric analyses indicated that population-level variation in P. graeca was mainly associated with differences in tissue dimensions of stem (periderm, collenchyma, cortex and vascular bundles) and mesophyll (palisade and spongy), and size and density of epidermal cells and stomata. Although some characters showed statistically significant differences, the overall anatomical, micromorphological and karyological similarity between the populations suggests that these differences are related to environmental variation rather than taxonomic differentiation.