Kazempour Osaloo, S. (Department of Plant Biology, Tarbiat Modares University, Tehran 14115-175, Iran; skosaloo@yahoo.com), A. A. Maassoumi (Department of Botany, Research Institute of Forests and Rangelands, Tehran 13185-116, Iran) & N. Murakami (Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan). Molecular systematics of the Old World Astragalus (Fabaceae) as inferred from nrDNA ITS sequence data. Brittonia 57: 367–381. 2005.—This study represents a nuclear rDNA ITS-based phylogenetic analyses of a greater sampling of the Old World Astragalus compared to our previous work (212 vs. 134 taxa). Phylogenetic relationships among 212 species (213 accessions) of the Old World Astragalus, including newly segregated monotypic genus Podlechiella, the two aneuploid New World Astragalus, and five related genera, were inferred from analyses of nuclear rDNA ITS sequences using maximum parsimony. A total of 658 nucleotide sites and four binary characters for indels were analyzed. The results of phylogenetic analyses suggest sect. Phyllolobium, comprising mostly the Chinese species, is placed outside of the so-called Astragalus s. str. and is a well-supported monophyletic group. The monotypic annual segregate genus Thlaspidium (≡Astragalus sect. Thlaspidium, A. thlaspi), is clearly nested within Astragalus s. str. Among the many sections analyzed here, only sects. Cenanthrum, Caraganella, Eremophysa, Incani, Laxiflori, and Lotidium are strongly supported as monophyletic. Our analysis, in agreement with previous studies, shows that the North American euploid Astragalus species are scattered throughout the Old World groups of the genus.