Pigments responsible for ultraviolet patterns in flowers of Oenothera (Onagraceae)

Abstract

MANY insect-pollinated flowers have nectar guides¹ which increase the foraging and pollination efficiency of their insect visitors². Some of these are visible only by their contrasting ultraviolet patterns, visible to insects but not to humans³. In such flowers, the nectar guides absorb ultraviolet light, and the compounds responsible were early suspected to be phenolics⁴. Recently, in Rudbeckia hirta L. (Asteraceae), a mixture of methylated flavonol glycosides has been shown to be responsible⁵. We report here that another class of flavonoids, chalcones, is responsible for the similar patterns in Oenothera (Fig. 1) and in three other genera of Onagraceae with flowers that appear uniformly yellow to humans.