AbstractThe polypeptide composition of the large and small subunits of ribulose‐1,5‐bisphosphate carboxylase/oxy‐genase (RUBISCO) fromCardaria draba(L.) DESV. (Brassicaceae) and from representatives of the related genusLepidiumL. have been studied by isoelectric focusing (IEF) analysis. In the literatureCardariaDESV. is either treated as a separate genus or as a section within the genusLepidium Cardaria draba(L.) DESV. and threeLepidiumtaxa of sectionLepia(DESV.) DC. are characterized by identical polypeptide patterns otherwise not found inLepidium. RUBISCO data would preliminarily suggest thatC. drabahas its closest relatives withinLepidiumsectionLepiaand therefore could possibly be placed best within this se