There is controversy about whether traditional medicine can guide drug discovery, and investment in bioprospecting informed by ethnobotanical data has fluctuated. One view is that traditionally used medicinal plants are not necessarily efficacious and there are no robust methods for distinguishing those which are most likely to be bioactive when selecting species for further testing. Here, we reconstruct a genus-level molecular phylogenetic tree representing the 20,000 species found in the floras of three disparate biodiversity hotspots: Nepal, New Zealand, and the Cape of South Africa. Borrowing phylogenetic methods from community ecology, we reveal significant clustering of the 1,500 traditionally used species, and provide a direct measure of the relatedness of the three medicinal floras. We demonstrate shared phylogenetic patterns across the floras: related plants from these regions are used to treat medical conditions in the same therapeutic areas. This finding strongly indicates independent discovery of plant efficacy, an interpretation corroborated by the presence of a significantly greater proportion of known bioactive species in these plant groups than in random samples. We conclude that phylogenetic cross-cultural comparisons can focus screening efforts on a subset of traditionally used plants that are richer in bioactive compounds, and could revitalize the use of traditional knowledge in bioprospecting.ethnobotany | ethnopharmacology | herbal medicine | phylogeny | systematics M any pharmaceutical drugs are derived from plants that were first used in traditional systems of medicine (1), and according to the World Health Organization ∼25% of medicines are plant-derived (http://www.who.int/mediacentre/factsheets/ fs134). Discoveries of novel molecules and advances in production of plant-based products (2, 3) have revived interest in natural product research. Traditional knowledge has proven a useful tool in the search for new plant-based medicines (4-8). The number of traditionally used plant species worldwide is estimated to be between 10,000 and 53,000 (9, 10); however, only a small proportion have been screened for biological activity (11,12) and the plants from some regions are less studied than others. For example, only 1% of tropical floras have been investigated (12). Moreover, there has been no systematic study to determine whether traditionally used species are significantly more likely to yield valuable bioactive compounds. This lack of data creates controversy about whether traditional medicine can guide drug discovery (1,11,(13)(14)(15), and investment in ethnobotanically led bioprospecting has fluctuated (5, 14, 15). Methods put forward for distinguishing those plants most likely to be bioactive when selecting species for further testing have been criticized, and criteria proposed to prioritize traditionally used species have not been rigorously tested (16,17). For example, use of the same or related plants by people from different regions and cultures provides indirect evidence for bioactiv...

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Adenogramma natans, a remarkable new aquatic species from Western Cape, South Africa.