Accessions representing a range of diversity in Brassica napus and their potential diploid progenitor species were analyzed using nuclear, chloroplast (ct), and mitochondrial (mt) RFLPs. Based on RFLPs of ctDNA and mtDNA, cytoplasmic genomes of the diploid species examined could be classified into four major types, represented by almost all B. rapa, Broccoletto (a specialized form of B. rapa), B. oleracea, and B. montana. Results from phylogenetic analyses of these data suggest that B. montana might be closely related to the prototype that gave rise to both cytoplasms of B. rapa and B. oleracea. The four major types of cytoplasms found in the diploid species were also observed in B. napus accessions. A majority of the cultivated B. napus examined contained a cytoplasm different from those of either B. rapa and B. oleracea. These B. napus accessions (designated M/N cytoplasm type) had the same chloroplast genome as that of B. montana and a unique mitochondrial genome that was somewhat intermediate between those of B. montana and B. rapa. These results strongly support the concept of multiple origins of B. napus and provide the first evidence that most cultivated forms of B. napus were derived from a cross in which a closely related ancestral species of B. rapa and B. oleracea was the maternal donor. Phylogenetic relationships based on nuclear RFLPs clearly separated B. napus accessions having different cytoplasm types, providing further evidence for multiple origins of B. napus. Brassica napus accessions having M/N type cytoplasm were clustered together as three subgroups: one contained oilseed cultivars from Canada, a second contained oilseed cultivars from Europe, and a third contained accessions of rutabaga.Key words: Brassica napus, molecular taxonomy, RFLP, chloroplast, mitochondrion.