ORIGIN AND BIOGEOGRAPHY OF AESCULUS L. (HIPPOCASTANACEAE) - A MOLECULAR PHYLOGENETIC PERSPECTIVE

Sequences of chloroplast gene matK and internal transcribed spacers of nuclear ribosomal RNA genes were used for phylogenetic analyses of Ae sculus, a genus currently distributed in eastern Asia, eastern and wes tern North America, and southeastern Europe. Phylogenetic relationship s inferred from these molecular data are highly correlated with the ge ographic distributions of species. The identified lineages closely cor respond to the five sections previously recognized on the basis of mor phology. Ancestral character-state reconstruction, a molecular clock, and fossil evidence were used to infer the origin and biogeographic hi story of the genus within a phylogenetic framework. Based on the molec ular phylogenetic reconstruction of the genus, sequence divergence, an d paleontological evidence, we infer that the genus originated during the transition from the Cretaceous to the Tertiary (similar to 65 M.Y. B.P.) at a high latitude in eastern Asia and spread into North America and Europe as an element of the ''boreotropical flora''; the current disjunct distribution of the genus resulted from geological and climat ic changes during the Tertiary.