An improved understanding of the phylogenetic history of the Fagaceae and Juglandaceae, two widespread members of the expanded Fagales clade, suggests several patterns of vicariance throughout the Tertiary of the Northern Hemisphere. The rich fossil record for these families also provides essential temporal data for calibrating phylogenies and comparing divergence times times among apparently similar patterns of vicariance. At least 4 genera of Fagaceae (Castanea, Fagus, Lithocarpus and Quercus) and two genera of Juglandaceae (Carya and Juglans) have disjunct distributions amenable to biogeographical analysis. Fagaceae show a successional pattern of discontinuity, perhaps starting with an ancient disjunction within Trigonobalanuss.l. More species-rich genera such as Fagus, Quercus, and Lithocarpuscontinue to support a center of origin in south east Asia with subsequent migration to western North America. Disjunction within the evergreen genus Lithocarpus(SE Asia-W N. Amer.) may suggest an exchange during warmer periods of the Eocene. In contrast, a close relationship between Fagus grandifolia(NA) and south east Asian species rather than Eurasian species supports a deciduous connection via the Bering Land Bridge. Fossil data also confirm the presence of Fagus in the Miocene of western North America. More recent connections, possibly via the Bering Land Bridge, but with the reverse pattern of migration, are indicated by the trans-continental white oaks (Quercussect. Quercuss.s.). For Juglandaceae, disjunctions within Caryaand Juglansappear to have occurred at different times: Caryashows no evidence of trans-continental disjunction at the sectional level, whereas Juglansshows one recent example within the butternut species group. In order to temporally discriminate among apparently similar vicariant patterns, divergence times were calculated with maximum likelihood methods that assume a molecular clock and alternative methods that permit constrained rate variation. Randomization tests were used to assess confidence intervals on divergence times, permitting rigorous tests of the sequence of biogeographic events.

Key words: biogeography, divergence times, Fagaceae, Fagales, Juglandaceae, vicariance