Diversification in species complexes: tests of species origin and delimitation in the Bursera simaruba clade of tropical trees (Burseraceae).

Molecular phylogenies are invaluable for testing morphology-based species delimitation in species complexes, as well as for examining hypotheses regarding the origination of species in these groups. Using five nucleotide markers, we reconstructed the phylogeny of the Bursera simaruba species complex of neotropical trees to test the notion that four "satellite" species originated from populations of the most widely distributed member of the genus, B. simaruba, which the satellites strongly resemble. In addition to molecular phylogenetic reconstruction, we tested species delimitation of B. simaruba and the satellites using multivariate analyses of morphological and ecological characters. The analyses evaluated the taxonomic value of these traditional characters and pinpointed those in need of further study, such as the expression of pubescence. Phylogenetic data rejected the origin of three satellite species from their purported ancestor, B. simaruba, and we ascribe their morphological similarity to convergence or parallelism. The fourth satellite species likely represents one end of a spectrum of inflorescence length variation within B. simaruba and is conspecific. Despite its marked morphological variability, we recovered B. simaruba as a single valid species, which implies that it maintains genetic cohesion among distant populations throughout its vast range.