Petiole micromorphology in Brassicaceous taxa and its potential for accurate taxonomic identification

Petiole anatomy is considered one of the important diagnostic characteristics that can be effectively employed in taxa discrimination at the species level. In this study, comprehensive petiole anatomy of 25 wild Brassicaceae taxa from Northern Baluchistan was carried out to examine variations in petiole anatomical features that are significant in the identification and delimitation of species. The current research first time reported Goldbachia pendula from Pakistan. The study also includes endemic taxa Farsetia hamiltonii. Variations observed among qualitative (shapes of petiole, epidermis, collenchyma, chlorenchyma, sclerenchyma, trichome, cuticle, xylem vessel, phloem, collenchyma, chlorenchyma, sclerenchyma, arrangement and several vascular bundles, presence/absence of pith, the sub-epidermal ring of collenchyma) and quantitative (diameter of petiole, pith, vascular bundles) characteristics of the petiole. Observed shapes of petiole were sulcate, flat, oval or circular with blunt or acute wings. Vascular bundles in petioles were collateral closed, collateral open, bi-collateral, or hadrocentric types with arrangements of single, 1 + 2 (one large central, two lateral) and numerous (2-20). The surfaces of petioles were marked with three types of trichomes unicellular, uniseriate, and multiseriate. Petiole of Physorrhynchus brahuicus was the largest (length 2561.8 mu m, width 2004 mu m). The highest numbers of vascular bundles (20) were observed in the Alyssum desertorum. Conringia orientalis possessed the largest pith (length 1711.6 mu m 850.4 mu m). The parameters were collected into a matrix and statistically analyzed the ability of variables to segregate taxa using Past 4.03. PCA clustering, UPGMA dendrogram revealed comparability and negative correlation at genus, among species of the same genus and distinct species. Via documentation of distinct microscopic petiolar anatomical variables, the study will be significant for the characterization and delimitation of taxa at genus and species level in the family Brassicaceae, the exploration of evolutionary and microclimatic effects on designing anatomy of taxa in distinct floristic regions.