Northern Hemisphere origins of the amphi‐Pacific tropical plant family Symplocaceae

Aim We sought to reconstruct the historical biogeography of the amphi-Pacific tropical disjunct plant family Symplocaceae in the context of competing Northern Hemisphere (boreotropical) versus Southern Hemisphere (West Gondwanan) hypotheses for its origin and spread. Location Americas, western Pacific Rim, fossil localities in Europe. Methods We derived a dated phylogeny using a relaxed clock on a data set of 114 terminals, four genic regions (three plastid regions and the nuclear ribosomal internal transcribed spacer region) and six fossil calibrations. We inferred ancestral geographical ranges with maximum likelihood under a dispersal–extinction–cladogenesis model, with the probability of dispersal constrained by areal distance and palaeogeography. Results We inferred a Eurasian origin for crown-node Symplocaceae at c. 52 Ma, followed by dispersal to North America (including Mesoamerica) at c. 52–38 Ma. Most of the highest likelihood intra-American dispersals recovered in the analysis trended from north to south, with none from south to north. Six intra-American dispersals were inferred to have originated in North America, with lineages either terminating in the Antilles or migrating to South America at various times. One additional North American lineage emigrated back to Eurasia in the late Miocene. Main conclusions The predominantly southwards American migrations inferred here for the Symplocaceae conform to the boreotropics hypothesis, apparently driven by cooling and drying climates in the later Cenozoic. The inferred Eurasian origin for the family corroborates a more specific European origin, as suggested independently by its fossil fruit record. Of the lineages ultimately arriving in South America from North America, two are inferred to have migrated through the Antilles (by island-hopping) and three through Mesoamerica. The timing of one of the Mesoamerican events, inferred to be between 8.9 and 7.5 Ma, implies over-water dispersal under the prevailing model of Isthmus of Panama formation, but also accords with overland migration under a model of earlier formation.