The influence of the Gondwanan breakup on the biogeographic history of the ziziphoids (Rhamnaceae)

Aim We investigated whether the fossil‐rich and cosmopolitan buckthorn family (Rhamnaceae, dating back to the Cretaceous) was influenced by vicariance events following the Gondwanan breakup. To answer this question, we focused on the ziziphoid lineage of the buckthorn family, because extant ziziphoid taxa comprise tribes and genera exclusively or at least predominantly distributed in the Southern Hemisphere (Australia, Africa, and South America). Location World‐wide. Methods We generated a DNA alignment of 26,989 bp (from plastid, mitochondrial, and nuclear genomes), comprising 575 taxa of Rhamnaceae and related families, including all major lineages within Rhamnaceae and closely related families. We used nine internal fossils to set constraints in our molecular dating analyses. We used ‘BioGeoBEARS’ in R to reconstruct ancestral areas in order to infer the impact of vicariance events on the ziziphoids caused by Gondwanan fragmentation. Results Our biogeographic analyses illustrate that the ziziphoid lineage was influenced by both long‐distance dispersal and Gondwanan breakup vicariance events. Yet, these vicariance events cannot explain all divergence events at the backbone of this lineage. Main conclusions Our study highlights that a taxon's distribution throughout the Northern Hemisphere can be the result of vicariance, but this process may be obliterated by more recent long‐distance dispersal (LDD). Our study also highlights that sufficiently old taxa may sometimes constitute better models to investigate the impact of Gondwanan‐driven vicariance than taxa with a current disjunct distribution in the Southern Hemisphere.