Phylogenetic inference in section Archerythroxylum informs taxonomy, biogeography, and the domestication of coca (Erythroxylum species).

Abstract

This investigation establishes the first DNA-sequence-based phylogenetic hypothesis of species relationships in the coca family (Erythroxylaceae) and presents its implications for the intrageneric taxonomy and neotropical biogeography of Erythroxylum. We also identify the closest wild relatives and evolutionary relationships of the cultivated coca taxa. We focused our phylogenomic inference on the largest taxonomic section in the genus Erythroxylum (Archerythroxylum O.E.Schulz) using concatenation and gene tree reconciliation methods from hybridization-based target capture of 427 genes. We show that neotropical Erythroxylum are monophyletic within the paleotropical lineages, yet Archerythroxylum and all of the other taxonomic sections from which we sampled multiple species lack monophyly. We mapped phytogeographic states onto the tree and found some concordance between these regions and clades. The wild species E. gracilipes and E. cataractarum are most closely related to the cultivated E. coca and E. novogranatense, but relationships within this "coca" clade remain equivocal. Our results point to the difficulty of morphology-based intrageneric classification in this clade and highlight the importance of integrative taxonomy in future systematic revisions. We can confidently identify E. gracilipes and E. cataractarum as the closest wild relatives of the coca taxa, but understanding the domestication history of this crop will require more thorough phylogeographic analysis.