Micro-morphological study of three members of genus <i>Plectranthus</i> L. (Lamiaceae) in Nigeria

Abstract

Micro-morphological studies of three members of the Genus Plectranthus L. (Lamiaceae) in Nigeria were conducted to investigate the anatomical characteristics of taxonomic importance. The following plant samples were collected from various locations in Southwestern Nigeria, namely Plectranthus aegyptiacus (Forssk.) C. Chr., Plectranthus esculentus N.E.Br. and Plectranthus monostachyus (P. Beauv.) B. J. Pollard. The anatomical study of the lamina epidermis, venation pattern and petiole were performed. The Single Linkage Cluster Analysis (SLCA) and one-way Analysis of Variance (ANOVA) with the Duncan Multiple Range Test (DMRT) were used to analyze the parameters, and photomicrographs were employed to document the observations. Foliar epidermal characteristics such as epidermal cell shape, anticlinal wall pattern, stomata types, trichome types and ergastic substances are essential in delimiting the species. The identification of numerous starch grains delimits P. monostachyus from the other species, a straight anticlinal wall pattern delimits P. esculentus, and the presence of abundant crystal sands delimits P. aegyptiacus. Quantitatively, stomata index (S.I.) and trichome length for both adaxial and abaxial surfaces were significantly different (P≤0.05) among the species. The venation pattern of the studied plant samples also revealed specific characteristics. Irregular vein spacing, eucamptodromous secondary vein category and polygonal areole shape delimit P. esculentus from the other species.