Forty-eight rhizobial isolates from root nodules of Indigofera and Kummerowia, two genera of annual or perennial wild legumes growing in the Loess Plateau in north-western China, were characterized by a polyphasic approach. Two main groups, cluster 1 and cluster 2, were defined based upon the results of numerical taxonomy, SDS-PAGE of whole-cell proteins and DNA relatedness. All the isolates within cluster 1 were isolated from Indigofera and they were identified as Rhizobium strains by 16S rRNA gene analysis. DNA relatedness of 29<5–48<9% was obtained among the cluster 1 isolates and the reference strains for defined Rhizobium species. Cluster 2 consisted of isolates from Kummerowia stipulacea and was identified as belonging to Sinorhizobium by 16S rRNA gene analyses. DNA relatedness varied from 5<2 to 41<7% among the isolates of cluster 2 and reference strains for Sinorhizobium species. Considering the existence of distinctive features among these two groups and related species within the genera Rhizobium and Sinorhizobium, we propose two novel species, Rhizobium indigoferae sp. nov. for cluster 1, with isolate CCBAU 71714T (=AS 1.3046T) as the type strain, and Sinorhizobium kummerowiae sp. nov. for cluster 2, with isolate CCBAU 71042T (=AS 1.3045T) as the type strain.