Commiphora of the highlands and escarpments of Angola and Namibia
Keywords:Angola, Commiphora, escarpments, evolution, highlands, Namibia
The myrrh genus, Commiphora Jacq. (Burseraceae), comprises approximately 190 species of trees and shrubs worldwide that are most commonly encountered in the seasonally dry and arid biomes of sub-Saharan Africa. The diversity of Commiphora species in southwestern Africa is notable for its many restricted-range species, including nine that were only discovered within the last two decades. Of the 36 species native to the region, the majority (29 species) are endemic or near-endemic to Angola and/or Namibia and 22 species occur at elevations of 1,000 masl or greater. Molecular phylogenetic data reveal that early divergences within the genus probably involved exchanges between southwestern Africa and Madagascar beginning in the Miocene, and that extant species in southwestern Africa arose from several different evolutionary lineages. Some species divergences within the largest radiation of southwest African endemic species appear to be associated with elevational disjunctions or latitudinal disjunctions between the Kaokoveld and Gariep centres of endemism, some of which are hypothesised to have occurred as recently as the Quaternary. Despite Commiphora being renowned for its fragrant oleoresins and ethnobotany, fundamental aspects of Commiphora’s systematic biology, ecology and evolution remain understudied. Many species have yet to be included in molecular phylogenetic analyses. Other major avenues for investigation include characterising species’ anatomical and physiological abilities to withstand the extreme heat and the water deficit of their natural environment; their reproductive ecology; and the chemical ecological interactions mediated by the diverse secondary chemistry of their oleoresins. Future research priorities include exploratory fieldwork to document the species of Commiphora in Angola, collaborative efforts to improve biodiversity informatic resources for the genus and integrative approaches to expand our understanding of Commiphora’s ecology and evolution within a comprehensive phylogenomic framework.
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