The historical biogeography of Fagaceae: Tracking the tertiary history of temperate and subtropical forests of the Northern Hemisphere

The angiosperm family Fagaceae is a central element of several distinct com munity types throughout the Northern Hemisphere and a prime candidate for m odern biogeographic analysis. The rich fossil record for the family provide s an unparalleled source to compare with modern distributions and evaluate hypotheses of origin, migration, and vicariance. We conducted separate phyl ogenetic analyses on genera with intercontinentally disjunct distributions using various noncoding regions of chloroplast and nuclear ribosomal DNA se quences. Analyses generally supported the (North America-(Europe+Asia)) pat tern area relationships. Divergence times between disjunct species were est imated to aid in the development of a comparative synthesis of historical b iogeography across the family. Fully resolved phylogenies were analyzed bio geographically using three distinct approaches: dispersal-vicariance analys is (DIVA), strict vicariance, and dispersal analysis using Fitch parsimony. Ancestral area reconstructions based on DIVA were preferred because event- based inferences generally were consistent with fossil evidence for migrati on and estimates of divergence times. Reconstructions suggested an Asian or igin for the genus Fagus with bidirectional migration to Europe and North A merica, consistent with a paraphyletic assemblage of Asian species and inte rcontinental exchange via the Bering Land Bridge (BLB). Reconstructions wit hin Quercus generally were more ambiguous in determining a center of origin ; however, one optimization pathway was consistent with the vicariance of a n ancestrally widespread distribution and the initial divergence between la rgely North American and Asian clades. Within the North American clade, dis persal to Eurasia is inferred for section Quercus (white oaks). Bidirection al floristic exchange via the BLB is supported for these temperate taxa, fo llowed by intercontinental disjunction by the mid-Miocene. In contrast, dis junctions based on living and fossil distributions within evergreen Fagacea e (e.g., Castanopsis, Lithocarpus, Trigonobalanus) suggest older, temporall y distinct biogeographic histories involving both the North Atlantic and Be ring Land Bridges.