Micromorphological Characters in Wild Medicinal Species of Dioscorea (Dioscoreaceae)

Abstract

Adulteration, misidentification, and substitution of wild Dioscorea species are common in Nigeria's herbal market and among traditional herbal practitioners. The present investigation reports a comparative micromorphological study of three wild species of Dioscorea L. used in ethnomedicine in South-western Nigeria to elucidate taxonomically significant characters, which would aid species identification. Physical and chemical methods were used in obtaining the epidermal leaf surfaces of the Dioscorea species. Leaves of D. hirtiflora Benth. and D. bulbifera L. were amphistomatic, whereas D. dumetorum (Kunth) Pax were hypostomatic. Diagnostic foliar epidermal characters include striated cell wall; presence of raphides in D. hirtiflora and D. dumetorum and secretory glands in D. dumetorum (wild) and D. hirtiflora. Glandular trichomes were observed in all species in addition to simple, elongated, unicellular trichomes in D. dumetorum and stellate trichomes in D. hirtiflora. Epidermal cells mainly were polygonal, straight to slightly wavy but deeply undulating in D. dumetorum. The largest and smallest mean epidermal cell sizes were obtained on the adaxial surfaces of D. bulbifera (mauve) and D. dumetorum (wild), respectively. Micromorphological characters in the Dioscorea species studied are taxonomically significant for species identification and could serve as diagnostic taxonomic tools for their standardization. A key for the identification of species is provided.