Chemosystematic studies on the genus Scalesia (Asteraceae)

摘要

Leaf samples of 13 of the 15 known species of the genus Scalesia, endemic to the Galapagos Islands, were investigated in order to analyze their chemical constituents, particularly those accumulated in their capitate glandular trichomes. The use of micropreparative techniques was necessitated by the fact that only single leaves from herbarium specimens were accessible. HPLC analysis allowed the identification of 10 sesquiterpene lactones and three flavonoids by means of indirect peak assignment withauthentic reference compounds. Eudesmanolides in combination with guaianolides and xanthanolides characterized the terpenoid pattern of the genus. In addition, several taxa contained major amounts of the flavanone naringenin and two of its derivatives.Only one species, S. cordata, did not show any detectable compound. The compound patterns allowed differentiation between all investigated taxa. At the same time, variability among different populations of a taxon was low, even when they were derived from different islands of the archipelago. The combination of sesquiterpene lactone skeletal types found in Scalesia was so far unique for the Helianthinae and implications for intergeneric relationships are discussed.