In the Ord River irrigation area near Kununurra in the Kimberley region of Western Australia, symptoms suggestive of Bean common mosaic virus (BCMV) were found in a common leguminous weed, Macroptilium atropurpureum (siratro). Virus from one M. atropurpureum plant and an isolate from Phaseolus vulgaris (common bean) identified previously as BCMV based on genome fragment sequencing and host range, were both transmitted to Nicotiana benthamiana, Chenopodium amaranticolor and C. quinoa by sap inoculation, giving symptoms typical of BCMV. Reciprocal inoculations with infective N. benthamiana sap indicated that both source plants contained the same virus species and reproduced field symptoms consistent with BCMV in both original hosts. Complete (10054 nucleotide) and partial (∼8400 nucleotide) sequences were determined for two sub-isolates MS1 and NWA-1, respectively, using reverse transcriptionpolymerase chain reaction assays. Both sub-isolates were from a N. benthamiana plant containing a BCMV isolate originally from a single M. atropurpureum plant. Their nucleotide sequences were aligned with those of four complete and three partial BCMV genome sequences, and their coat protein amino acid sequences were aligned with those of 17 other BCMV isolates. The results from the genomic and coat protein analyses show that the two M. atropurpureum sub-isolates were closely related to BCMV isolates reported previously from North and South America.