WEN, JUN. Department of Biology, Colorado State University, Fort Collins, CO 80523. - The evolution of eastern Asian and eastern North American plant disjunctions: overview and perspectives from phylogenetic studies.
The eastern Asian and eastern North American plant disjunction is a
classical biogeographic pattern. This pattern was first noticed by
Linnaeus in 1750 and elaborated by Asa Gray in a series of papers
between 1840 to 1878. Approximately 65 genera of flowering plants are
confined to eastern Asia and eastern North America. Previous studies
reported a high level of morphological similarity among the disjunct
species and many intercontinental species pairs were proposed.
Morphological stasis has been suggested to be common among these
disjuncts. Recent phylogenetic analyses confirm the close affinity of
taxa in most disjunct genera, but few intercontinental sister-species
relationships have been detected. Several disjunct taxa are
polyphyletic or paraphyletic, suggesting that the morphological
similarities in these groups may be attributable to convergence or
symplesiomorphies. Subtropical and tropical taxa (e.g., in
Aralia) may be nested within the temperate disjuncts,
suggesting the need to examine the eastern Asian – eastern North
American disjunction in the context of global biogeography.
Phylogenetic patterns and results from morphometric analyses in
Aralia, Corylus, Osmorhiza, Panax, and
Prunus support morphological stasis of the eastern Asian and
eastern North American disjuncts via either evolutionary constraints
Key words: Biogeography, disjunction, eastern Asia, eastern North America, Northern Hemisphere biogeography