The species complex Targionia hypophylla-Targionia lorbeeriana includes a haploid and a triploid cytotype in Europe and the Atlantic islands. As shown by isozyme analysis, high levels of fixed heterozygosity and duplication of one of the chromosome sets characterize the triploids that are fertile. Hybridization between two haploids, followed by chromosome doubling and meiotic nondisjunction can explain triploidy. Both allopolyploidy and autopolyploidy are invoked for the origin of the triploid. The duplicated chromosome set most likely comes from the existing haploid that could be one of the putative parents. The morphological intergradation between the two cytotypes, their identical ecological requirements and sympatric distribution can be understood in the light of these data. A haploid Texan colony analyzed for comparison can be discarded as the other putative parent, which remains unknown. Moreover, three triploid African and Australasian colonies do not share the same duplicated genome as the triploids from Europe and the Atlantic islands. Electrophoretic data indicate independent origins of the European-Atlantic and African-Australasian polyploids.