Notes on the Burseraceae in central Amazonia, including four new taxa. Studies in neotropical Burseraceae XXVI

The Burseraceae are known to comprise one of the most important tree families in Amazonia, but examination of Burseraceae diversity indicates that this importance is achieved differently in different parts of the Amazon, generally showing greater relative density compared to relative diversity in the east and greater relative diversity compared to relative density in the west, but both high relative density and diversity in central Amazonia. The patterns of relative density may be explained by current climates and by soils, but those of diversity are more likely a function of historical events. Revision of the Burseraceae for two projects near Manaus, Brazil revealed four new taxa. Protium hebetatum is widespread in western Amazonia, but it is one of the most common trees in central and west-central Amazonia; it resembles P. grandifolium. Protium tonyanum is a distinctive new species in poorly resolved sect. Sarcoprotium. Protium paniculatum var. modestum is known thus far only from the vicinity of Manaus plus several localities in the state of Amazonas, Venezuela; a key to the varieties is provided. Dacryodes hopkinsii is one of a group of four species in that genus from Amazonia and the Venezuelan Guayana with relatively large and fleshy flowers that are functionally bisexual. The discovery of these new taxa underscores the biological importance of Manaus and vicinity as a center of diversity for many taxa and exemplifies the synergy between well-designed floristic projects and systematics.