Systematic Studies of the Burseraceae
Douglas C. Daly
The species of the Burseraceae comprise a modest-sized family of trees, but one that shows outsized importance in the Amazon region, Mexico, Southeast Asia, Tropical East Africa, and Madagascar, because in those regions it makes up many of the individual trees and/or species of their forests. Near Manaus, Brazil, some 10% of the individual trees are Burseraceae, and the single most common species is a Burseraceae. Some of this importance has been discovered only recently; in Madagascar, for example, the genus Canarium was believed to be represented by only two species, but after two collaborators (one a Malagasy botanist) and I studied the genus intensively in the field and herbarium for a number of years, our taxonomic revision revealed 33 species of Canarium on that island, 27 of them new to science. My work on Canarium made me realize that the genus needs an enormous amount of work in tropical Asia, where all but one of the remaining ca. 115 species occur, so I have already begun field and herbarium work in Southeast Asia.
The Burseraceae of Amazonia are now relatively well-studied, which makes the family an attractive model for studying processes of evolution and patterns of biogeography in that region. For example, a team that conducted molecular studies of the genus Protium showed that the evolutionary transition from clay soils to sandy soils occurred independently several times, and that speciation in these cases resulted over short distances via habitat shifts and not due to long-term isolation. We are now embarking on a study to decipher the processes and geography of Protium in the Andes, between the Amazon and another center of Burseraceae in the Pacific coastal forests of Colombia and Ecuador. This is taking place in the context of a taxonomic monograph of the entire tribe to which Protium belongs, tackling it section by section. Elsewhere in the family, I am working with a current Brazilian student on a revision of the Neotropical genus Trattinnickia, and with a former student from Colombia on a revision of the larger and more complex pantropical genus Dacryodes.