Fifty-five Chinese isolates form nodules of Amorpha fruticosa were characterized and compared with the type strains of teh species and genera of baceria which form nitrogen-fixing symbioses with teguminous host plants A polyphasic approach which inclued RFLP of PCR-amplifiod 165 rRNA genes, multiolcus enzyme elctrophoresis (MLEE) DNA-DNA hybrization 165 rRNA gene sequencing electrophorestic plasmid profiles cross-nodulation and a phenotypic study was used in teh comparatie analysis The isolated originated from several different sites in China and they varaied in their phenotypic and genetic characteristics The majority of teh isolates had moderate to slow growth rates produced acid on YMA and harboured a 930kb symbiotic plasmid (pSym) Five different RFLP patterns were idnetified among the 165 rRNA genes of all lthe isolates isolates grouped by PCR-RFLP of the 165 rRNA genes were also separated into groups by variation in MLEE profiles and by DNA-DNA hybrizdization A representatie isolate from each of these DNA homology groups had a separated position in a phylogenetic tree as determined from sequencing analyss of teh 165 rRNA genes A new species Mesorhizobium amorphae is proposed for th majority of the isolates which belonged to a moderatly slow-to slow-growing acid-producing group based upon their distinct hylogenctic position their unique electrophoretic type, their low DNA homology with reference strains representing the species within the genus Mesorhizobium and their distinct phenotypic features Strain ACCCC 19665 was cholsen as the type strain for M. amorphae sp. nov.