A total of 19 sesquiterpene lactones were isolated from roots of Lactuca canadensis L., of which 10 were reported for the first time from Lactuca species and two were unknown. This is also the first report on the co-occurrence of three pairs of zaluzanin C-type guaianolides, epimeric at C-3, and on
A new guaianolide and a new eudesmanolide were isolated from Lactuca tatarica, as well as eight known sesquiterpenoids. The new compounds were elucidated on the basis of spectroscopic methods including IR, HRESIMS, 1D and 2D NMR, and the known compounds were established by comparing their physical