The alkaloid contents of Argemone hispida Gray and A. munita Dur. & Hilg. subsp. rotundata (Rydb.) G. B. Ownb. have been established and compared with other Argemone species in a search for biogenetic and chemotaxonomic relationships. A new alkaloid, munitagine, has been isolated from A. munita and its structure has been shown to be 2,7-dihydroxy-3,9-dimethoxy-5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene-N-methyl-6,12-imine. This represents the first alkaloid of the dibenzocyclooctene group to exhibit an altered substituent pattern. The structures of all alkaloids of this group, including munitagine, can be correlated with that of reticuline, which was found to occur in both species.