Earlier students of the origin of Lotus corniculatus suggested that this tetraploid species arose as an autotetraploid of the closely related diploid species L. tenuis or L. alpinus. More recent studies suggested that L. alpinus and L. japonicus could be ancestral forms. The present study of tannin content, phenolic content, cyanide production, morphology, cytogenetics, Rhizobium specificity and self-incompatibility in the corniculatus group virtually excludes the possibility that L. corniculatus could have arisen through autopolyploidy of L. tenuis or L. alpinus, and suggests that L. corniculatus arose through hybridization of L. alpinus and/or L. tenuis (probably as female parent) with L. uliginosus (probably as male parent), followed by chromosome doubling in the hybrid.