ALLAN, GERARD J.*, ELIZABETH A. ZIMMER, AND WARREN W. WAGNER. Laboratory of Molecular Systematics, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560. - Biogeographic relationships between western North American and Mediterranean floras: insights from molecular phylogenetic studies of tribe Loteae (Faboideae: Fabaceae).
Mediterranean regions are some of the most unique and biologically
fascinating areas on the face of the Earth. Corresponding largely to
the Cape region of South Africa, central Chile, southwest and southern
Australia, California and the borders of the Mediterranean Sea, these
five regions exhibit remarkable similarities in climate, topography
and flora and fauna. How similarities in the flora and fauna arose,
however, has been a question of considerable interest and debate. The
discovery of the underlying phylogenetic relationships of organisms
inhabiting these areas can lead to an increased understanding of their
evolution and diversification. In this study, we investigate the
biogeography of two groups of morphologically similar plant taxa that
occupy two different mediterranean regions: western North America and
mediterranean Eurasia. Taxa of the two groups were sequenced for the
ITS1, 5.8S and ITS2 regions of nuclear ribosomal DNA and their
phylogenetic relationships were estimated using parsimony. We are
also investigating the phylogenetic utility of the trnL region
of cpDNA. Evidence based on ITS, however, suggests that the largest
taxon, Lotus, is not monophyletic, but is composed of separate
western North American and Eurasian clades. This suggests that the
morphological similarities observed between Old and New World
Lotus are either the result of convergence or are
symplesiomorphic. Mapping of the character "region" onto the
phylogeny suggests a complex biogeographic scenario involving multiple
dispersals from Eurasia to western North America, followed by back
dispersal to Eurasia. This dispersal pattern suggests a series of
multiple, intercontinental dispersals that involve not only
Lotus, but the Eurasian taxon Coronilla as well. These
results provide insight into the evolution of morphological
similarities in tribe Loteae, and yield a preliminary framework for
assessing the biogeography of other temperate legume taxa occupying
disjunct mediterranean regions
Key words: Biogeography, ITS, Loteae, phylogeny