Spring is fast approaching and children will soon be waving buttercups under your chin to see if you like butter – but what causes their unique yellow glow?
Scientists from the University of Cambridge have discovered that the distinctive glossiness of the humble buttercup – Ranunculus repens – is related to its unique anatomical structure. The buttercup petal’s unique bright and glossy appearance is the result of interplay between its different layers.
“This phenomenon has intrigued scientists and laymen alike for centuries,” said Dr Beverly Glover from the Department of Plant Sciences. “Our research provides exciting insight into not only a children’s game but also the lengths to which flowers will go to attract pollinators.”
The researchers investigated the petals spectroscopically and correlated the optical results with the layered anatomy of the petal. The strong yellow reflection responsible for the chin illumination is caused by the epidermal layer of the petal reflecting yellow light with an intensity comparable to glass.
The epidermal layer has two extremely flat surfaces from which light is reflected – the top of the cells and an air gap between the epidermis and the lower levels of the petals. This effectively doubles the gloss of the petal, which is why buttercups are better at reflecting light under your chin than any other flower.
Buttercups were also found to reflect a significant amount of UV light. Since many pollinators have eyes sensitive in the UV region, this provides insight into how the flower uses its unique appearance to attract insects.
“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,” said Dr Silvia Vignolini from the Department of Physics. “Moreover, the glossiness might also mimic the presence of nectar droplets on petals, making them much more attractive.”
The work has been published in The Royal Society journal Interface.