Leaf and stem anatomy of Micromeria species from the Central part of the Balkan Peninsula

The anatomical structure of the leaf and stem of nine Micromeria species from the Balkan Peninsula was investigated with the aim to establish the adaptive characteristics and traits that could be useful in the identification of species and subgeneric classification. The species included in the anatomical analysis were: Micromeria albanica (Griseb. ex K. Malý) Silic, M. thymifolia (Scop.) Fritch, M. pulegium (Rochel) Bentham, M. dalmatica Bentham of section Pseudomelissa and M. cristata (Hampe) Griseb., M. kosaninii Silic, M. juliana (L.) Bentham ex Reichenb., M. croatica (Pers.) Schott M. parviflora (Vis.) Reichenb. of section Micromeria. Variability of 17 quantitative characters of the leaf (thickness, height of adaxial and abaxial epidermis, thickness of the palisade and spongy tissue) and stem (radius, cortex thickness, thickness of the vascular cylinder, phloem, xylem, pith radius) was examined. Multivariate analysis of variance (ANOVA), principal component analysis (PCA), canonical discriminant analysis (CDA) and UPGMA clustering method based on Mahalanobis’ distances were used to determine the variability structure and level of importance of the anatomical differentiation of the investigated taxa. Qualitative characters were also included in the consideration of the anatomical variability, such as leaf shape, leaf margin, position of sclerenchyma fibers in the leaf and stem. The results showed that investigated Micromeria species posses a xeromorphic general structure plan, but each species has achieved distinctive adaptations according to its specific genetic potential. The results have shown a clear difference between the species belonging to the different sections of genus Micromeria, so they have a potential diagnostic and systematic value.