Phylogeny reveals non-random medicinal plant organ selection by local people in Benin

Humans rely on plants in their environment for food and medicine. Understanding how humans select plant species will help us anticipate what plant species will be valuable for society in the future. However, previous approaches to study the drivers of plant selection have been criticized. We explored medicinal plant selection using a refined methodology and corroborate that humans select plant species for medicine in a non-random way. Furthermore, we found that selection of specific plant organs across similar species is also non-random. Improved understanding of medicinal plant selection can help identify new medicinal plants and the particular organs of plant species that are most likely to contain bioactive compounds to help improve human health and well-being. Summary: Ethnobotany, the science of human–plant interactions, has for long focused on documenting the traditional knowledge that humans have developed and accumulated over centuries toward plant uses. However, how such knowledge is constructed remains poorly understood and some of the methodological approaches developed for this purpose have been criticized. Here, we combine negative binomial models and phylogenetic comparative methods to test whether selection of medicinal plant species and organs by local people are non-random using data from Benin, a country in West Africa with roughly 3,000 plant species. We found evidence for taxonomic and phylogenetic non-random selection of medicinal plants: some taxa are preferentially used for medicine. Our analysis uncovers that plant organs are also non-randomly selected for medicine. Beyond plant taxonomy, similar plant organs of closely related species tended to be used for similar treatments because these organs are likely to have similar secondary chemistry. Such non-random organ selection was more apparent for certain plant organs such as roots, bark, and leaves, which are predicted to be more vital for population fitness and species persistence. Collectively, our study suggests that the emerging non-random pattern of medicinal plant selection may be a consequence of heterogeneous within-plant distribution of secondary chemistry across different organs proportionally to their importance to plant fitness as predicted by the optimal defense theory.