Molecular systematics of the neotropical dragon's blood trees Croton sect. Cyclostigma (Euphorbiaceae)

The species of Croton section Cyclostigma, popularly known as dragon's blood, are used medicinally throughout Latin America. We examined the monophyly and phylogenetic relationships of sect. Cyclostigma sensu Webster using sequences of nuclear ribosomal ITS and plastid spacer trnL-F. The two gene phylogenies concurred that sect. Cyclostigma as traditionally delimited is not monophyletic, with its members appearing in nine different clades throughout Croton. A clade retaining almost half of the sampled species including the type of the section was designated as sect. Cyclostigma s.s. The recircumscribed section appears to be strictly Neotropical. The phylogenetic position of sect. Cyclostigma s.s. within Croton remains unclear.; Phylogenetic relationships within Croton sect. Cyclostigma s.s. were inferred using DNA sequences from three gene regions (nuclear ribosomal ITS and chloroplast trnL-F and matK). The plastid (combined trnL-F + matK ) and ITS phylogenies show some topological conflicts, indicating that chloroplast capture or reticulate evolution might have played a role in the evolutionary history of sect. Cyclostigma. The analysis of the three molecular data sets together recovered a monophyletic Cyclostigma s.s with two major clades. All the species from southeastern Brazil, with the exception of C. urucurana, were recovered in a clade sister to a northern Andean clade, which together were sister to a southern Andean clade. Cladistic analysis of morphological traits using parsimony largely contradicted the molecularly delimitated sect. Cyclostigma s.s.; Phylogenetic relationships and genetic variation within species of the lechleri clade were also examined. Croton lechleri ranges along the eastern Andes from southern Colombia to northeastern Bolivia, and it has been suggested that it is part of a species complex along with C. draconoides and C. urucurana from the eastern Amazon, and the Brazilian Shield respectively. Our results suggest that C. draconoides originated from an ancient hybridization event. Based on the molecular phylogeny, morphological data, reticulate evolution, and biogeography, Croton lechleri, C. urucurana, and C. draconoides are retained as distinct species. ITS sequences of C. urucurana are very uniform across its geographical range whereas the morphological variability of C. lechleri is reflected in the phylogenetic structure of the different lechleri accessions in the ITS phylogeny.