9407824 Sanderson The flowering plant genus Astragalus, of the legume family, containing upwards of 2500 species worldwide, is a remarkable example of rapid evolutionary diversification on a global scale. Reconstructing the evolutionary relationships or phylogeny within such a genus can provide clues as to why it is so ecologically successful. However, the technical and logistical problems associated with phylogenetic analyses of large genera have prevented significant progress in understanding relationships within Astragalus. One promising approach is to identify major subgroups, establish the phylogenetic status of these (whether they are monophyletic), and then reconstruct their relationships to each other. The present study will evaluate three phylogenetic hypotheses regarding one large putative monophyletic group within Astragalus. This group consists of a series of some 500 species distributed in the New World, which all possess an unusual chromosome complement (they are aneuploids) that differs from the rest of the genus. The three hypotheses are (1) that all New World aneuploids form a monophyletic group distinct from rare Old World aneuploids and equally rare New World euploids; (2) that Old World aneuploids represent evolutionarily independent origins of the aneuploid chromosome condition; and (3) that New World euploids are not the closest relatives of New World aneuploids, rather they are more closely related to Old World species. Evidence from mutational differences in nuclear ribosomal and chloroplast DNA will be gathered from hundreds of New and Old World species, and integrated with chromosome counts and morphological features. Efforts will be made to detect reliable morphological characters associated with the origin of the aneuploid groups in the New and Old World.
