Chemosystematic studies on the genus Scalesia (Asteraceae)

Leaf samples of 13 of the 15 known species of the genus Scalesia were inves tigated in order to analyze their chemical constituents, particularly those accumulated in their capitate glandular trichomes. The use of microprepara tive techniques was necessitated by the fact that only single leaves from h erbarium specimens were accessible of these plants, endemic to the Galapago s Islands. HPLC analysis allowed the identification of 10 sesquiterpene lac tones and three flavonoids by means of indirect peak assignment with authen tic reference compounds. Eudesmanolides in combination with guaianolides an d xanthanolides characterized the terpenoid pattern of the genus. In additi on, several taxa contained major amounts of the flavanone naringenin and tw o of its derivatives. Only one species, S. cordata, did not show any detect able compound. The compound patterns allowed differentiation between all in vestigated taxa. At the same time, variability among different populations of a taxon was low, even when they were derived from different islands of t he archipelago. The combination of sesquiterpene lactone skeletal types fou nd in Scalesia is so far unique for the Helianthinae and implications for i ntergeneric relationships are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.