A family-level floristic inventory and analysis of medicinal plants used in Traditional African Medicine

Abstract

Ethnopharmacological relevance: Floristic diversity patterns of medicinal plants in sub-Saharan Africa are compared to global patterns to gain insights into the selection of plants used in Traditional African Medicine.

Aims of the study: To answer two questions: Firstly, is the selection of medicinal plants used in Traditional African Medicine in sub-Saharan Africa based on availability or is it biased towards certain plant families? Secondly, does the floristic composition of African medicinal plants differ from the global pattern and from other healing systems of the world?

Materials and methods: Data edited and summarized from recent reviews and on-line databases were compiled into an inventory of all vascular plant families of the world, showing the global numbers of species per family, the numbers of African taxa per family, the numbers of African medicinal plant species per family and the numbers of commonly traded African medicinal plants. These data were subjected to linear regression analyses, as well as Bayesian analysis and Imprecise Probability calculation (using the Imprecise Dirichlet model).

Results: At least 4576 vascular plant species from 1518 genera are used in Traditional African Medicine in sub-Saharan Africa, representing 192 families (out of 254 African families). Traditional African Medicine is dominated by Fabaceae (567 spp., 156 genera), Rubiaceae (318 spp., 99 genera), Asteraceae (314 spp., 112 genera), Malvaceae (202 spp., 46 genera), Euphorbiaceae (197 spp., 47 genera), Apocynaceae (167 spp., 68 genera), Lamiaceae (142 spp., 37 genera), Acanthaceae (106 spp., 40 genera), Asparagaceae (90 spp., 18 genera) and Poaceae (85 species, 47 genera). Regression analysis of the African medicinal flora shows that the Fabaceae (576 medicinal species/residual +136), Malvaceae (202/+105), Rubiaceae (318/+85), Lamiaceae (142/+55), Euphorbiaceae (197/+54) and Combretaceae (72/+49) are overused, while Aizoaceae (10/-136), Orchidaceae (34/-127), Iridaceae (16/-101) and Poaceae (85/-87) are underused. Bayesian and IDM analysis showed that a large number of smaller families are also overused and underused. Commonly traded African medicinal plants species are mostly from Fabaceae (27 species), Apocynaceae (16), Burseraceae (12) and Rubiaceae (9).

Conclusion: The selection of African medicinal plants appears to be based on availability (for some families) and apparently cultural and other criteria, such as the presence of alkaloids, terpenoids and volatile compounds for others (e.g., Fabaceae, Apocynaceae and Burseraceae). In terms of commercialised species in international trade, Traditional African Medicine differs from the global pattern (and other healing systems) in the dominance of Fabaceae and Apocynaceae and the relatively low numbers of Asteraceae, Lamiaceae, Apiaceae and Rosaceae.

Keywords: African medicinal flora; Bayesian analysis; Commercialised medicinal plants; IDM analysis; Linear regression analysis; Sub-saharan Africa.