Flavonoids and verbascoside as chemotaxonomic characters in the genera Oxera and Faradaya (Labiatae)

Most known species belonging to the closely related genera Oxera and Faradaya (Labiatae) were investigated for their caffeic acid conjugates anti flavonoids. Verbascoside was detected in all species, varying from very high concentrations in Faradaya and the Oxera pulchella-group, to trace amounts in the O. neriifolia-group and O. sulfurea. Rosmarinic acid was absent. The most common flavonoids in both genera were 7-O-glucuronides of flavones. In addition,more than 50% of the species contained flavones glycosylated in the B-ring. Flavone C-glycosides were restricted to Faradaya, the O. neriifolia-group and O. crassifolia, whereas O. coriacea contained a flavonol glycoside. No 6-hydroxylated flavones were found, which are characteristic flavonoids in the related genus Clerodendrum in which Faradaya was formerly included. On the whole, the range of phenolics was very similar in Oxera and Faradaya, but in Oxera total flavonoid levels were more or less equal to or higher than those of verbascoside-type compounds, whereas in Faradaya the latter were much higher. Ratios of the levels of flavonoids and verbascosides also correlated with informal classification within Oxera mainly based on morphological characters, as did presence of flavone C- and certain di-O-glycosides. (C) 1998 Elsevier Science Ltd. All rights reserved.