Information about the symbionts of legumes of the Caesalpinioideae subfamily is still limited, and we performed a polyphasic approach with three strains-CNPSo 3448, CNPSo 3394 and CNPSo 3442-isolated from , a native legume broadly distributed in the USA. In the phylogenetic analysis of both the 16S rRNA gene and the intergenic transcribed spacer, the CNPSo strains were clustered within the superclade. Multilocus sequence analysis with six housekeeping genes-, , , , and -indicated that is the closest species, with 83 % of nucleotide identity. In the genome analyses of CNPSo 3448, average nucleotide identity and digital DNA-DNA hybridization results confirmed higher similarity with , with values estimated of 93.35 and 51.50 %, respectively, both below the threshold of the same species, confirming that the CNPSo strains represent a new lineage. BOX-PCR profiles indicated high intraspecific genetic diversity between the CNPSo strains. In the analyses of the symbiotic genes and the CNPSo strains were clustered with , , , and , indicating a different phylogenetic history compared to the conserved core genes. Other physiological (C utilization, tolerance to antibiotics and abiotic stresses), chemical (fatty acid profile) and symbiotic (nodulation host range) properties were evaluated and are described. The data from our study support the description of the CNPSo strains as the novel species sp. nov., with CNPSo 3448 (=USDA 10051=U687=CL 40) designated as the type strain.