The monophyly of Bursera and its impact for divergence times of Burseraceae

Bursera is one of the most diverse and abundant groups of trees and shrubs of the Mexican tropical dry forests. Its interaction with its specialist herbivores in the chrysomelid genus Blepharida, is one of the best-studied coevolutionary systems. Prior studies based on molecular phylogenies concluded that Bursera is a monophyletic genus. Recently, however, other molecular analyses have suggested that the genus might be paraphyletic, with the closely related Commiphora, nested within Bursera. If this is correct, then interpretations of coevolution results would have to be revised. Whether Bursera is or is not monophyletic also has implications for the age of Burseraceae, since previous dates were based on calibrations using Bursera fossils assuming that Bursera was paraphyletic. We performed a phylogenetic analysis of 76 species and varieties of Bursera, 51 species of Commiphora, and 13 outgroups using nuclear DNA data. We also reconstructed a phylogeny of the Burseraceae using 59 members of the family, 9 outgroups and nuclear and chloroplast sequence data. These analyses strongly confirm previous conclusions that this genus is monophyletic. New calculations of the age of Burseraceae date the beginning of its diversification to at least 93 million years ago.