DONOGHUE, MICHAEL J.*, CHARLES D. BELL, AND JIANHUA LI. Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138 and Department of Ecology and Evolutionary Biology, Yale University, New Haven, CN 06511, Arnold Arboretum of Harvard University, Jamaica Plain, MA 02130. - Reconciling phytogeographic patterns around the Northern Hemisphere.
Traditional vicariance analyses of the Northern Hemisphere are
destined to be confusing by virtue of mixing splitting events that
occurred at different times. To avoid this problem it would be wise
to sort phylogenies according to lineage divergence times and then
analyze subsets of trees that are relevant to the same time
period/vicariance events. As a starting point in this sorting
process, we recognize two major tracks around the Northern Hemisphere:
an Atlantic track characterized by species in China, Europe, and
southeastern North America, and a Pacific track involving China,
Japan, often western North America, and eastern North America. Here
we concentrate on our recent analyses of clades showing the Pacific
track. All possible patterns of relationship involving North America,
Japan, and China appear among the groups we have considered. North
American species are most closely related to Japanese species in
Hamamelis and Viburnum sect. Pseudotinus. North
American species are linked with one or more Chinese species in
Triosteum and Buckleya, to the exclusion of the Japanese
species. In Torreya it appears that the Chinese and Japanese
species form a clade to the exclusion of the North American species.
These differences either imply different vicariance events in
different time periods, or differential responses to the same
vicariance events coupled with extinction. We explore both
possibilities, bringing estimated divergence times to bear on the
problem when possible.
Key words: Asia, biogeography, divergence times, North America, Northern Hemisphere, phylogeny