The genus Dugesia, included in the tribe Heliantheae (Compositae) was not previously studied for chemical composition. A root extract of D. mexicana was analyzed, and no acetylene compounds were found, but a sesquiterpene lactone, C15H20O2, was isolated, for which the NMR spectrum suggests an eremophilane derivative, such as was previously discovered only in the tribe Senecioneae. A careful restudy of the taxonomic position of this genus may therefore be desirable.