Rupert Barneby and his legume legacy
Wojciechowski, Martin F. .
Astragalus: a molecular phylogenetic perspective.
Nucleotide sequences of the plastid matK gene and nuclear ribosomal DNA internal transcribed spacer region were sampled from Astragalus (Fabaceae), and several of its closest relatives within tribe Galegeae, to infer phylogenetic relationships and estimate the ages of their diversification. Consistent with previous studies that emphasized sampling for nrDNA ITS primarily within New World or Old World species groups of the genus, Astragalus, with the exception of a few morphologically distinct species, is strongly supported as monophyletic based on maximum parsimony and Bayesian analyses of matK sequences as well as a combined matK+ITS dataset. The matK data also provides better resolution and stronger clade support for relationships among Astragalus and traditionally related genera than nrDNA ITS. Astragalus plus the genera Oxytropis and Biserrula are strongly supported as sister to a clade composed of strictly Old World (African, Eurasian, Australasian) taxa including the genera Colutea, Sutherlandia, Lessertia, Swainsona, Clianthus and Carmichaelia. This larger Astragalean clade is one of three well-supported subclades that comprise the monophyletic group of temperate herbaceous legumes marked by the loss of one copy of the inverted repeat in the chloroplast genome. The ages of these clades and rates of nucleotide substitution estimated from a fossil-constrained, rate-smoothed, Bayesian likelihood analysis of more than 330 matK gene sequences sampled throughout the entire family indicate Astragalus and Oxytropis diverged from their African-Eurasian sister groups ca. 15 Ma, and Astragalus diverged from Oxytropis at least 10 Ma. The mean rate of nucleotide substitution for matK among Astragalus and sister groups, with estimates that range from 7.7 to 8.3 x 10^-10 substitutions per site per year, is approximately an order of magnitude slower than that estimated for the nuclear ITS region.
1 - Arizona State University, School of Life Sciences, PO Box 874501, Tempe, Arizona, 85287-4501, USA
nrDNA ITS sequences
Presentation Type: Symposium
Location: Magpie (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 2:15 PM