CHEMOTAXONOMIC ANALYSIS OF PAPPOBOLUS (ASTERACEAE, HELIANTHEAE)

Chemical constituents from capitate glandular trichomes were analyzed for 33 of the 38 species of Pappobolus. In total, 35 HPLC peaks were detected, 30 of which could be tentatively assigned to known compounds of the sesquiterpene lactone and benzofuran type. Compounds of the 1-keto-2,3-unsaturated-furanoheliangolide type (budleins) were present in all plants and quantitatively dominated the compound patterns. Several other heliangolides were also present. Xanthanolides were detected in about 50% of the species, and benzofurans from about two-thirds of them. Pappobolus is the only genus for which benzofurans have been demonstrated to occur in capitate glandular trichomes. Overall there was a high degree of chemical homogeneity, which is in accord with the suggestion that Pappobolus is monophyletic and of relatively recent origin. Pappobolus is distinct from other genera of the subtribe Helianthinae in the occurrence of xanthanolides and in the lack of germacrolides and eudesmanolides.