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.

Collection of the plant materials: All the plant materials used in the study has been collected from the Maharaja Sayajirao University Campus, Waghai Botanical Garden (Gujarat state) and Botanical Garden of the Shivaji University, Kolhapur (Maharashtra State) except Schnella guianensis (Aubl.) Wunderlin. The details of voucher specimens are given in Table 1. Petiole of the fully-grown leaves (15 to 20^th leaf from the apex) having similar age were collected from species of Bauhinia s.l. and fixed in FAA (Formalin - Acetic acid- Alcohol 10:5:85, v/v) (Berlyn and Miksche 1976). For each species, 25 petioles (i.e., five petioles from five individuals each) from different populations were collected. All the species were either growing naturally in wild or they were under cultivation in the botanical garden of the Maharaja Sayajirao University of Baroda, Vadodara (Gujarat), Waghai Botanical Garden (Forest Department, Government of Gujarat) and the botanical garden of the Shivaji University, Kolhapur. After 24-36 hrs of fixation, they were transferred into 70% alcohol for further processing and storage.

Anatomical preparations: For the paraffin processing, the central portions of the petioles were cut into 2-3 mm long pieces and dehydrated through Tertiary Butyl Alcohol (TBA) series and processed by the routine method of paraffin embedding (Johansen 1940). Central portions of the petiole from the fully grown and mature leaves were utilised for histological investigations. Serial transverse and tangential longitudinal sections of 10-15 µm thick were obtained using the rotary (Leica RM 2035) microtome. The sections were stained with safranin Astra blue combination (Srebotnik and Messener 1994). After passing through the ethanol xylene series, they were mounted in Dibutyl Phthalate Xylene (DPX). Sections were observed under Leica (DM 2000) trinocular research microscope and micro-photographs for important results were taken with Leica DFC 295 firewire digital camera.