A review of Neotropical Burseraceae

This review of Neotropical Burseraceae emphasizes developments since the last major review of the family in 2011. The Burseraceae comprise a Laurasian group (represented by Eocene fossils in the Northern Hemisphere) that originally dispersed through Central America into Amazonia. During cooling and drying events in the Oligocene, the frost-intolerant northern American progenitors were likely driven extinct; subsequently, the family experienced several vicariant events and later several long-distance dispersals across the Southern Hemisphere. From Amazonia, the family re-colonized Central America and the Caribbean. The most rapid diversifications in the Americas for the Burseraceae occurred during the Miocene in Protium and Bursera, much of it through geological events, dispersal, and habitat specialization. A number of taxonomic advances were made in Neotropical Burseraceae since 2011; these included 59 published new species overall, re-drawn generic limits in tribe Protieae, new genus records for Burseraceae in Central America and the Cerrado of Brazil, new taxa that more than doubled the number of Neotropical Dacryodes, and a recently recognized center of diversity for Protium in the Andes. Revised generic descriptions and a new key to the New World genera of Burseraceae are provided. Special attention is given to the implications of leaf architecture for characterization of clades. Monoecy (rare) and parthenocarpy (possibly frequent) are discussed, and the close relationship of dioecious trees and small bee pollination is highlighted. Most Burseraceae are dispersed by birds or arboreal mammals that carry pyrenes relatively short distances away from the mother tree; however, other modes are found in the family, including wind dispersal (rare in New World Burseraceae), clumped dispersal of pyrenes by ants and lizards, and oilbirds that can disperse Dacryodes fruits more than 30 km; some dispersers that ingest pyrenes also aid in germination. The diversity and abundance of Burseraceae in a number of regions and habitats (but especially in moist forests of Amazonia and dry forests of Mexico) are striking. This, plus the fact that the taxonomy and phylogeny of New World Burseraceae are relatively well-resolved, spotlights the Burseraceae as an important model organism for researching mechanisms of diversification, species limits, cryptic species, and “hyperdominance” in tropical forests. High chemical diversity and differences in biological activity make sense in the context of diversification and coexistence. Studies of chemical defenses support the idea of a “growth defense trade-off” and suggest that selection by different natural enemies could be implicated in the speciation process; they also show that closely related species often display high chemical divergence, and plants with the most chemical defenses have a lower number and diversity of insect herbivores. The range of physical and chemical properties of Burseraceae resin is reflected in their cultural uses, which are diverse while showing strong ethnobotanical convergence.