Several strains isolated from Cytisus villosus nodules have been characterized based on their diverse genetic, phenotypic and symbiotic characteristics. According to 16S rRNA gene sequence analysis, the isolates formed a group that was closely related to Bradyrhizobium canariense BTA-1(T) with 99.4% similarity. Analysis of three housekeeping genes, recA, atpD and glnII, suggested that the C. villosus strains represent a novel Bradyrhizobium species most closely related to B. canariense BTA-1(T) with similarities of 94.2, 96.7 and 94.5%, respectively. All these differences were congruent with DNA-DNA hybridization analysis, which revealed 31% relatedness between a representative strain (CTAW11(T)) isolated from C. villosus nodules and B. canariense BTA-1(T). Phenotypic differences among the strains isolated from C. villosus and B. canariense were based on assimilation of carbon and nitrogen sources. The nodC and nifH genes of strain CTAW11(T) were phylogenetically related to those of strains belonging to bv. genistearum and divergent from those of bv. glycinearum and, accordingly, they do not nodulate soybean. Based on the genotypic and phenotypic data obtained in this study, our strains should be classified as representatives of a novel species for which the name Bradyrhizobium cytisi sp. nov. is proposed; the type strain is CTAW11(T) (=LMG 25866(T)=CECT 7749(T)).