Boffins have discovered the real reason why buttercups glow yellow under your chin – and it’s nothing to do with whether you like butter.
Experts and plant scientists from Cambridge University have found the unique glossiness of the flower – made popular by the children’s game of shining it under their chins – is related to its anatomical structure.
The findings, published today in the Royal Society journal Interface, reveal the flower’s appearance is the result of interplay between the petals layers.
The yellow reflection which becomes evident when the flower is held close to the skin is due to the epidermal layer of the petal which reflects light with an intensity comparable to glass.
According to the study, the epidermal layer of cells has not one but two extremely flat surfaces from which the light is reflected.
One rests on the top of the cells, while the other exists because the epidermis is separated from the lower layers of the petal by an air gap.
The gloss of the petal is thus effectively doubled as the reflection of light occurs on the smooth surface of the cells and on the layer of air.
Researchers also found the diminutive yellow flower reflects a significant amount of UV light. This helps the buttercup to attract insects as many pollinators, including bees have eyes sensitive in the UV region.
Dr Beverley Glover, Department of Plant Sciences, said: “This phenomenon has intrigued scientists and laymen alike for centuries. Our research provides exciting insight into not only a children’s game but also into the lengths to which flowers will go to attract pollinators.”
Professor Ulli Steiner, from the Nanophotonics Centre at the Cavendish Laboratory, the University of Cambridge’s Department of Physics, said: “It is fun to revisit a problem that is more than one century old and, using modern methods, discover something new. The strong collaboration between Physics and the Plant Sciences has enabled this.”