Although some Lythraceae species have been investigated for alkaloidal content, no structural investigation has been carried out on this plant family. We have undertaken an investigation of Lythraceae in hopes of finding alkaloids with unique structures and physiological activity. In this paper we wish to report structure studies on the alkaloids of Decodon verticillatus (L.) Ell. ("water oleander" or "swamp loosestrife"), a plant which occurs in moderate amounts in some swampy areas near Tallahassee. Seven alkaloids have been isolated from Decodon verticillatus (L.) Ell. All are pentacyclic and contain the following structural features: a six-membered or greater lactone ring, the ether oxygen of which is derived from a secondary alcohol; a tertiary nitrogen atom; and two nonconjugated aromatic rings substituted with methoxyl and/or hydroxyl groups. Two of the alkaloids, vertine and verticillatine, have an additional olefinic bond located between one of the aromatic rings and the lactone carbonyl. This suggests that the lactone carbonyl group is gamma with respect to an aromatic ring in all Decodon alkaloids. The other alkaloids, with the possible exception of decaline and vertaline, may be represented by II also except that the cinnamic ester double bond is saturated. The data are consistent with II as the part structure for vertine and verticillatine.