FLAVONOID CHEMISTRY AND SYSTEMATICS OF TITHONIA (COMPOSITAE)

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Abstract
Twenty‐four flavonoid compounds, including chalcones and aurones, are reported from 13 taxa of Tithonia. Pedunculin (4′, 6, 7‐trimethoxy, 5, 8‐dihydroxyflavone), also is characterized. The distribution of these compounds is compared to the existing classification of the genus based primarily on morphological data. By comparison with the previously proposed phylogeny of the genus, the evolution of the flavonoid system may be elucidated. It is proposed that the ancestral stock of Tithonia had flavonols, di‐ and tri‐methoxyflavones, and 6‐methoxyflavones. From this ancestral stock, a number of trends have occured in derivative taxa. These trends are: 1) a maintenance of a diversity of compounds in several evolutionary lines, 2) a reduction in the number of methoxyl substitutions, and 3) the elaboration of 5‐deoxyflavones and flavonols.
Funding Information
  • National Science Foundation (DEB‐7618763)