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

1. Ethnobotany, the science of human-plant interactions, has for long
focused on documenting the traditional knowledge that humans have
developed and accumulated over centuries towards plant uses. However, how
such knowledge is constructed remains poorly understood and some of the
methodological approaches developed for this purpose have been
criticized.  2. 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.  3. 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 organs selection was more apparent for plant
organs such as roots, bark and leaves which are predicted to be more vital
for population fitness and species persistence.  4. Collectively,
our study suggests that the emerging non-random pattern of medicinal plant
selection may be a consequence of heterogenous within-plant distribution
of secondary chemistry across different organs proportionally to their
importance to plant fitness as predicted by the optimal defence
theory.