Petiole anatomy of some species of Bauhinia L. sensu lato (Leguminosae Juss.) occurring in India

Abstract

The petiole is a vital part of the leaf that acts as a bridge between the lamina and stem or branch for the transport of photosynthate, minerals, nutrients and provide flexible mechanical support to the lamina. Its anatomy remains unique and species‐specific. Therefore, twelve species of Bauhinia sensu lato were investigated histologically in the present study. The disparities in the petiole outline, structure and composition of secondary xylem and presence of cell inclusions can be wisely employed for species identification. Conducting elements of the xylem and phloem were arranged as irregularly distributed individual vascular bundles in Schnella guianensis. Several vascular bundles joined to form a double ring of the xylem and phloem in Piliostigma foveolatum, P. malabaricum, P. racemosum, two species of Phanera (P. retusa, P. vahlii) and Bauhinia variegata while in the remaining species, it remained as a single ring. Other features of taxonomic importance are xylem ring that can be circular and complete and if incomplete crescent‐shaped or ‘U' shaped, arrangement of cortical bundles and their position, accumulation of tannin etc. Deposition of tannin was observed in the pith, xylem and phloem parenchyma of Piliostigma foveolatum, P. malabaricum, Bauhinia tomentosa and B. variegata and in the pith and phloem parenchyma of Phanera phoenicea, Piliostigma racemosum and Phanera scandens. Tannin was found absent in B. acuminata and B. purpurea. All these features played important role in species recognition. Structural details of the petiole are described in detail for all the investigated species using standard anatomical methods and light microscopy. Findings revealed that anatomical characteristics of the petiole are of taxonomic value for this genus and can be valuable for species identification and classification.