The current range of Castanea Mill., a Tertiary disjunct genus with about seven species, includes eastern and western Asia, Europe, and eastern North America. The similarity between the forests of eastern Asia and eastern North America has been of interest to botanists since the time of Linnaeus. The disjunct taxa involved are hypothesized to have undergone restriction of a formerly continuous range during the Tertiary period, nearly 15 million years ago. At that time a global cooling and drying trend forced temperate forests to migrate southward. We sequenced cpDNA region matK and its surrounding spacers for all seven Castanea species, and the sequence data were used to construct a phylogenetic hypothesis for the genus. Percent sequence divergence between species of Castanea varies from 1.6 to 4.0%. Phylogenies generated by this work indicate that the previously proposed intrageneric classification systems within Castanea do not reflect the evolutionary relationships of the constituent species. Mapping the distribution of these plants onto the phylogenies generated by this study supports a complicated biogeographic history for this disjunct genus. The distribution of these plants has been thought to be the result of a simple range restriction, but our data support a more complicated history of repeated migrations, resulting from a combination of geographic and climatic factors.

Key words: biogeography, Castanea, disjunct, Fagaceae, matK, Tertiary