The use of geological and paleontological evidence in evaluating plant phylogeographic hypotheses in the Northern Hemisphere tertiary

Phylogeography posits that the sequence of speciation events within a clade should parallel the geographic migration and isolation of members of the clade through time. The primary historical features that govern migration and allopatry in land plants are changes in physical geography (e.g., oceans, mountains, and deserts) and in climate (e.g., moisture, temperature, and day length), features that are often interrelated. If we assume that living genera retain physiological stability through time, much as they retain the morphological features that allow their identification, then these environmental features of the geologic past may be used to test phylogeographic hypotheses of living genera based on phylogenetic analysis. The history of the climatic and geographic features of the Tertiary of the Northern Hemisphere agrees with many phylogenetically based phylogeographic hypotheses of living angiosperm genera but indicates that some hypotheses require reanalysis. While the parallel comparison of phylogenetic hypotheses and historical biogeographic evidence is in its infancy, the reciprocal illumination of the two approaches shows great promise for future application.