Genetic analysis of unusual complex-heterozygous genotypes in populations ofO. grandiflora from Alabama (USA) has shown that these strains are composed of a typicalgrandiflora (B) complex and an altered B complex (designated as BA) which probably contains genetic elements derived from an A genotype such as the beta complex ofO. biennis group 1. Analysis of the meiotic configurations of artificial hybrids between the new strains and a series of complexes of known segmental arrangement allowed determination of the arrangements of the unknown complexes. These data are evidence for origin of the altered B complexes.