Reflectance Measurements of Glossy Petals of Ranunculus lingua (Ranunculaceae) and of Non-Glossy Petals of Heliopsis helianthoides (Asteraceae)

Abstract: A spectrophotometric comparison of the reflectance of glossy petals of Ranunculus lingua (Ranunculaceae) and non-glossy petals of Heliopsis helianthoides (Asteraceae) was made in relation to the angle of incidence of the incoming light. Additionally, the reflectance of petals of R. flammula, R. acris and R. repens (Ranunculaceae) was measured for comparative purposes. In the examined Ranunculus species, gloss is present around mirror geometry over the whole spectral range measured, including the UV region where it accentuates the UV peak, and even at the basal UV-absorbing area of the petals. According to a colour hexagon evaluation of the reflectance data, these gloss phenomena diminish the colour contrast of the petal against the background. Nevertheless, due to their brightness, they may serve as an attractant or predictor for pollinators and other visiting insects, possibly acting as a beacon while approaching the flower. The position of the reflectance maximum in the UV around 340 nm is in accordance with the sensitivity maximum of the UV photoreceptor of potential pollinators like Apidae. The mean reflectance values of the four examined Ranunculus species do not show any clear correlation with their anatomical make-up