Diversification of yellow-flowered Sempervivum (crassulaceae) species from the Balkan Peninsula: Evidence from the morphometric study of the epidermal structures of rosette leaves

Several related yellow-flowered houseleek species which occur on the Balkan Peninsula are divided into two complexes: Sempervivum ciliosum (S. ciliosum, S. jakucsii, S. klepa, S. octopodes, and S. galicicum) and the S. ruthenicum complex (S. ruthenicum, S. leucanthum, S. kindingeri, and S. zeleborii). Due to strong phenotypic plasticity and a limited number of studies, it is difficult to assert at this point whether all the above species are well defined in the taxonomic sense. Detailed studies of the epidermal structures have not been conducted for any of the species in either complex. The aim of this study was to investigate the degree of variability of the epidermal structures together with their potential usefulness for the taxonomic characterization of the species studied. A total of 18 quantitative characters of the epidermal structures of the adaxial and abaxial surfaces of the rosette leaves were analysed within 16 populations. In all species, the epidermal cells are polygonal or irregularly shaped, with straight or sinuous anticlinal walls, while the rosette leaves are amphistomatic with anisocytic stomata. Simple biseriate multicellular glandular trichomes were found on the adaxial and abaxial surfaces and the margins of the rosette leaves. The results of the descriptive statistics, univariate (ANOVA) and multivariate statistical analysis (CDA, AHC) showed low to high variability in the epidermal cells, guard cells and trichomes. The multivariate analysis showed diversification among the complexes and species. The length of the marginal and apical trichomes of the rosette leaves contributed most to diversification.