Reflectance measurements of glossy petals of Ranunculus lingua (Ranunculaceae) and of non-glossy petals of Heliopsis helianthoides (Asteraceae)

A spectrophotometric comparison of the reflectance of glossy petals of Ranu nculus lingua (Ranunculaceae) and non-glossy petals of Heliopsis helianthoi des (Asteraceae) was made in relation to the angle of incidence of the inco ming light. Additionally, the reflectance of petals of R. flammula, R. acri s and R repens (Ranunculaceae) was measured for comparative purposes, in th e examined Ranunculus species, gross is present around mirror geometry over the whole spectral range measured, including the UV region where it accent uates the UV peak, and even at the basal UV-absorbing area of the petals. A ccording to a colour hexagon evaluation of the reflectance data, these glos s phenomena diminish the colour contrast of the petal against the backgroun d. Nevertheless, due to their brightness, they may serve as an attractant o r predictor for pollinators and other visiting insects, possibly acting as a beacon while approaching the flower. The position of the reflectance maxi mum in the UV around 340 nm is in accordance with the sensitivity maximum o f the UV photoreceptor of potential pollinators like Apidae. The mean refle ctance values of the four examined Ranunculus species do not show any clear correlation with their anatomical make-up.