Plant medicine, stimulant and cultural keystone: applying a herbariomics approach to explore the adoption of the coca plant by humans

Native to the South American tropics, coca (Erythroxylum coca and E. novogranatense) is a crop plant with which humans have had a relationship for at least 8,000 years. It is cultivated for its leaves which produce a multitude of alkaloids, famously including cocaine. This composite of alkaloids confers stimulatory, medicinal and nutritional properties and, combined with the entrenched ritual around leaf-chewing, coca retains an important place in the culture of millions of South Americans. Nonetheless, our botanical understanding of coca, e.g. in terms of its taxonomy and chemical ecology, remains patchy. This in turn hinders interpretation of its domestication process, with the two cultivated species separated by a pre-human timing of divergence and the possibility of more than two origins. Furthermore, the subtle domestication syndrome, typical of perennial tree crops and further underscored by the predominantly clonal propagation of coca, is non-trivial to characterise. Here, we present a herbariomics approach to delimiting diversity within the gene pool of coca and its wild relatives. To this end, we extracted genomic and biochemical data from ~200 Erythroxylum herbarium specimens to gain new insights into how E. coca and E. novogranatense adapted to human landscapes and were dispersed within them. Progressing research on the coca crop is timely, given the current discourse around legality of the coca leaf and sovereignty of Indigenous coca biodiversity in the context of coca monocultures and deforestation driven by the illegal cocaine market.