Comparative morphoanatomical analysis of the leaves and stems of Daphne (Thymelaeaceae) species

A study on the morphological variability and ecological differentiation among the species in the genus Daphne was carried out which included seven species from the Balkan Peninsula: Daphne mezereum, D. laureola, D. alpina, D. oleoides, D. malyana, D. cneorum and D. blagayana. In the Balkan Peninsula, the ranges of the species in this genus overlap, which does not occur anywhere else in Europe. Descriptive statistics were measured for 20 quantitative characters of the leves and stems. A comparative analysis of the morpho-anatomical adaptations of these species shows that: D. cneorum, D. malyana and D. oleoides belong to the adaptive type of xerophytes; D. alpina is a xeromesophyte; D. blagayana and D. laureola are mesoxerophytes; and D. mezereum is a mesophyte. Principal component analysis shows the largest contribution to the formation of the variability between the different species is made by characters that are related to leaf shape (leaf length, distance between the largest leaf width and the leaf top, largest width of the leaf, leaf surface area), followed by surface area of abaxial stomata, stem characters (stem cortex thickness and stem diameter) and leaf anatomy characters (thickness of the palisade tissue, thickness mesophyll, number of palisade layers). These features can use to discriminate among the seven studied species, suggesting that leaves and stems of Daphne can represent a source for taxonomically useful characters. Canonical discriminant analysis and the clustering method based on Mahalanobis distances shows that there is significant morphological differentiation among the species studied. The results show that various combinations of morphological and anatomical features contribute to the adaptive capacity of plants to different degrees. The morpho-anatomical features found in all seven species agree with previous infrageneric taxonomic classifications of this genus.