High potential of the genus Allanblackia (Guttiferae): Phytochemistry, pharmacology, and traditional uses over the past half-century

Abstract

The genus Allanblackia is part of the flowering plants of the Guttiferae family, with all its ten species growing across the rainforest belts of West, Central and East Africa. Allanblackia species have the largest fruits of all plants in the African rainforest. They are evergreen, dioecious, and medium-sized trees with average heights in the range 25–40 m and can produce more than 250 fruits per year. Their stem barks are reddish-brown, with small circular or rectangular scales over small red pits. The trunk is straight, cylindrical, without buttresses but sometimes basally thickened; with numerous branches and longitudinal grooves. Leaves are opposite, simple and entire; while flowers are unisexual, fragrant, and of pink/red or white/cream colour. Fruits are large, ellipsoid berries 10–50 cm × 15 cm in size, with five longitudinal ridges, while seeds are ovoid 3 cm × 2 cm × 1.5 cm. In addition to the numerous uses of Allanblackia in traditional medicine, the consumption and commercial exploitation of its seed oils are of great current interest. However, to date, there is no literature review collating the traditional uses, phytochemistry and biological activities of this genus. Therefore, the present review aims to provide a current, relevant and comprehensive summary of the botany, ethnomedicinal uses, phytochemistry, and biological activities of plants of the genus Allanblackia over the past half-century (1971 to 2021). To this end, a review of all published literature was conducted using various online scientific databases. According to the findings, the Allanblackia species are mostly used in folk medicine for the management of infectious and respiratory diseases. Chemical analysis of the genus Allanblackia revealed that xanthones and biflavonoids represent 51% and 16% of the total secondary metabolites, respectively and could therefore be considered as taxonomic markers of the genus. Extracts and isolates from some species of this genus were reported to exhibit promising antimicrobial, antileishmanial, anticholinesterase and cytotoxic activities, and therefore are vital enough to deserve further attention in new drug discovery.