Boreotropical migration explains hybridization between geographically distant lineages in the pantropical clade Sideroxyleae (Sapotaceae).

To determine whether the fragmented pantropical distribution of present day Sideroxyleae primarily is the result of long-distance dispersals or represents the remnants of a once continuous distribution in the northern hemisphere, the boreotropical flora, we used phylogenetic analyses of chloroplast and nuclear ribosomal DNA data, Bayesian molecular dating, and Bayesian estimation of ancestral areas. Incongruence between the two data sets was examined with a nuclear low copy gene phylogeny to discover any occurrences of reticulate evolution. The Pacific clade Nesoluma was shown to have two distinct copies of the nuclear low copy gene AAT, one from an African and one from an American ancestral lineage, indicating that it is of allopolyploid origin. We conclude that Sideroxyleae, including the ancestral lineages of Nesoluma, were part of the boreotropical flora and entered the New World via the north Atlantic land bridge. We also suggest that the distribution of extant species resulted from the cooling climate at the end of the Eocene. Sideroxylon oxyacanthum is shown not to belong in the group, but in Chrysophylloideae. A classification reflecting phylogenetic relationships, as well as new combinations for the species in Nesoluma under Sideroxylon, is presented.