Petiole anatomical features in Salix and some of its relatives in the family Salicaceae

The classification of the genus Salixis troubled by the intraspecific flexibility and diversity of the morphological features. The aim was to prepare a comparative description of petiole anatomy of 23 species of Salix, in addition to two species of Populus and Bivinia jalbertii, as well as to determine the taxonomic importance of petiole features. In order to do so, 10 quantitative and 10 qualitative petiole anatomical features were studied. Moreover, a Bayesian analysis was executed on the relevant ITS sequences obtained from GenBank, included 28 specimens from 17 species. The anatomical features were then mapped on the resulted cladogram and the ancestral states of some prominent petiole anatomical features were reconstructed. Based on the results, no stomata were observed in the petiole’s epidermis of any of the species studied; therefore, it could be assumed that, the petiole in the studied species is dependent to the leaf blade for respiration and gas exchange. While the quantitative petiole anatomical features were turn to be variable in the individuals of the same species grown in different habitats, qualitative features showed a desirable consistency. The petiole anatomical features studied were proved to be useful in the differentiation and identification of taxa at subgeneric and specific levels. In addition, the reconstruction of the ancestral state of the studied features revealed that, polygonal cell shape, straight or slightly curved anticlinal wall pattern, horizontal compression of the petiole, the presence of lateral ribs, convex adaxial surface and ribbed petiole outline were primitive features in the species studied.