Abstract
Twenty-seven flavonoids, 11 glycosides and 16 aglycones, were detected in Macaronesic Sideritis species. Flavonoid glycosides of three structural types were identified: 5-7-dihydroxyflavone 7-glycosides, 8-hydroxyflavone 7-glycosides and flavonoid p-coumaroylglucosides. Fourteen of the flavonoid aglycones were externally located on the leaf surfaces. Flavonoid aglycones were the main flavonoid constituents of the species included in section Empedocleopsis and in S. infernalis. The rest of the studied species produced, if any, only trace amounts of external flavonoid aglycones. Regarding the flavonoid glycosides, two different phytochemical groups were found among the species included in section Marrubiastrum. The first group contained 8-hydroxyflavone glycosides and the second was devoid of these substances. Phytochemical differences between the flavonoids produced by Mediterranean and Macaronesic Sideritis supported the division of the genus into two subgenera ( Sideritis and Marrubiastrum), but do not support their treatment as two different genera.
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