Abstract

SCANNING ELECTRON AND LIGHT MICROSCOPIC CHARACTERS RELATED WITH TAXONOMIC TREATMENT OF THE MEDICINAL PLANT POGOSTEMON BENGHALENSIS (BURM.F.) KUNTZE IN COMPARISON TO PACHOULI (LAMIACEAE)

Pradeep D. P and Murugan K.*

ABSTRACT

Taxonomic significance of the epidermal hairs and their systematic value in phylogenic relationship is well documented in Lamiaceae and related families such as Rutaceae, Verbenaceae, Scrophulariaceae and Acanthaceae. Many species of Lamiaceae produce therapeutic potential essential oils, which are synthesized and accumulated within glandular hairs on the leaf surface. The taxonomic values of epidermal hairs are confusing because of the varying terminology employed and also lack of full diversity of the epidermal hair spectrum. The usual and most evaluated of these glandular epidermal hairs are peltate (production and storage of essential oil) and capitate hairs (production of polysaccharides and minor levels of essential oil). Pogostemon is an economic significant medicinal herb due to its essential oils. Histological investigations of the secretory hairs of Pogostemon benghalensis and P. cablin leaves were carried using light and scanning electron microscopy. Glandular hairs are two types in P.benghalensis, i.e. longstalked capitate and round-shaped peltate hairs, whereas, in P. cablin the glandular hairs are diverse types. Non-glandular hairs are multicellular, linear and pointed. The findings are discussed in relation to documented trichomes from other members of the Lamiaceae. Nonglandular hairs are more abundant on leaf veins, particularly on the abaxial surface of young leaves and decreasing in numbers with age of the leaves. Capitate trichomes were observed only on the abaxial leaf surface, while peltate trichomes were distributed on both dorsal and ventral surfaces of leaves.

Keywords: Capitate, Electron microscopy, Epidermal hairs, Essential oil, Glandular, Nonglandular hairs, Peltate, Pogostemon, Phylogeny.