A taxonomic analysis of the Sudanese medicinal plant, Vachellia nilotica L. (syn: Acacia nilotica L.) based on pods, seeds, and vegetative traits

Abstract

Vachellia nilotica L. (Syn: Acacia nilotica) has puzzled taxonomic history and nomenclature. This study aimed to update the taxonomy of this species in the Sudan by identifying its subspecies and morphological differences among them. The study was carried out during the period from March 2020 to September 2022. The included collection sites were Riverine Forest s, seasonal streams, seasonal rivers, natural reserved forests, and natural areas out of reserved forests. The species phenology (vegetative growth, flowering, fruiting, and seeding time) was considered to facilitate delineation between its sub-taxa in each site during field surveys and data collection, which was done in 100 randomly selected circular plots (1000 m 2 ). Morphological characterization of the vegetative parts (16 traits) and pods and seeds (14 traits) was studied on 100 trees selected randomly for each identified sub-taxa in each site. The results indicated for the first time a new group intermediate in all studied morphological characteristics between the subspecies nilotica and tomentosa which were also identified in this study beside the subspecies adstringens. Furthermore, analysis of variance showed significant (P = 0.0001) variation among them in vegetative, pod, and seed characteristics. Pod shape, color, and texture; seed shape and size and number of pinnae per leaf were key features to distinguish between the subspecies and the new group. This study gave evidence for the first time for a new morphological group of Vachellia nilotica L. (Syn: Acacia nilotica) with intermediate characteristics of pods, seeds, and leaves and habit between subspecies nilotica and tomentosa at the mature stage, indicating potential hybridization among the subspecies.