Microscopical and histochemical assessment of Secamone emetica (Apocynaceae) Leaves -An endemic medicinal plant

Abstract

Secamone emetica (Apocynaceae), a climber native to South India and Sri Lanka, is traditionally used for nervous disorders, yet its anatomy and biochemical composition of leaves remain underexplored. Hence this study provides the first detailed anatomical and histochemical analysis of its leaves. The leaf samples were sectioned using a rotary microtome and stained with suitable reagents. Cleared leaves treated with chloral hydrate were analyzed for micromorphology, while powder microscopy involved sieving and microscopic observation of powdered fragments. Micromorphology revealed polygonal epidermal cells with thick, straight anticlinal walls and hypostomatic anomocytic stomata. The midrib showed a convex-concave structure with a uniseriate epidermis, subepidermal collenchyma, parenchymatous ground tissue with idioblasts and a bicollateral crescent-shaped vascular bundle. The dorsiventral lamina contained palisade and spongy parenchyma, druse crystals and laticifers. The petiole exhibited a canaliculate structure with a bicollateral vascular bundle and idioblasts. Histochemical analysis identified tannins in ground parenchyma and idioblasts, while alkaloids were in idioblasts, parenchyma near vascular bundles and ground tissue beneath the epidermis of the leaf and petiole. Starch and mucilage were in the central midrib and petiole, with resin and lignin in their piths. The lamina and petiole contained druse crystals, oil globules and stone cells. The hypostomatic leaves had an epidermal cell count of 510 ± 20/mm² (upper) and 760 ± 30/mm² (lower), stomatal density of 70 ± 7.07/mm² and a palisade ratio of 15.5 ± 3.54. Powder microscopy showed epidermal fragments, palisade parenchyma, reticulate vessels and latex tubes. These findings provide key diagnostic features and bioactive compound localization, aiding in species identification and quality control.