Systematic implications of sesquiterpene lactones in the subtribe melampodiinae

Within the tribe Heliantheae of the Asteraceae, the genetic boundaries of the subtribe Melampodinae have recently been drastically revised by Stuessy. The number of genera within the subtribe has been reduced and new generic groupings have been established. The present study correlates the distribution of sesquiterpene lactones found in these genera with the newly revised subtribal boundaries. The genera Acanthospermum, Melampodium, Polymnia and Sigesbeckia produce predominantly melampolide-type sequiterpene lactones. Limited chemical data support Stuessy's removal of the genera Desmanthodium, Clibadium and Ichthyothere from the subtribe Melampodiinae. The occurrence of melampolide-type sesquiterpene lactones in members of the genera Tetragonotheca (Helianthinae) and Enhydra (Ecliptinae) indicate a possible position of these genera in the Melampodiinae.