The reason why buttercups glow The researchers discovered that the buttercup petal's bright and glossy appearance is the result of the interplay between its different layers. The strong yellow reflection responsible for the chin illumination is mainly due to the epidermal layer of the petal that reflects yellow light with an intensity that is comparable to glass. The researchers also found that the buttercup reflects a significant amount of UV light. As many pollinators, including bees, have eyes sensitive in the UV region, this provides insight into how the buttercup uses its unique appearance to attract insects. Scientists had previously shown that the reflected colour is yellow due to the absorption of the colours in the blue-green region of the spectrum by the pigment in the petals. Dr Silvia Vignolini, from the university's department of physics, said: "Although many different factors, such as scent and temperature, influence the relationships between pollinators and flowers, the visual appearance of flowers is one of the most important factors in this communication. Flowers develop brilliant colour, or additional cues, such as glossiness - in the case of the buttercup - that contribute to make the optical response of the flower unique. Moreover, the glossiness might also mimic the presence of nectar droplets on the petals, making them that much more attractive.