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The buttercup’s chin-brightening yellow glow is more than child’s play – it gives the flower a competitive edge in attracting pollinators. But what causes this buttery gleam?

, at the University of Cambridge, and colleagues separated the layers that make up buttercup petals– an inner layer of starch and an outer epidermal layer that holds the yellow pigment– and shone light onto each. The starch layer reflected light like a rose petal, diffusing rays in many directions.

The key to the buttercup’s glow seems to lie in the exceptionally flat cells of its epidermal layer. Steiner’s team found that , like a flat mirror. This directed light creates an intense glow not seen if you hold another flower to your chin.

Magnifying this effect is an air pocket between epidermal and starch layers, the team also found. This keeps a portion of the incoming light from reaching the starch layer, ensuring that it is reflected in a directional manner by the flat cells at the base of the epidermal layer.

The reflectivity was the same for ultraviolet light, which bees use to navigate. As the buttercup sways in the wind, its petals flash like neon signs advertising its pollen.

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