The secret behind the buttercup's shine: Thin layer of film just one-cell thick reflects light to help petals glow
- The petals have a thin layer of cells on the outside called the epidermis
- This thin layer acts as a thin optical film, and light is reflected on both sides
- As the cell layer is very smooth, the reflected colours merge
- This creates a white sheen which makes the petals seem glossy
It's one of the classic games played in playgrounds around the world - putting a buttercup under your chin to determine whether or not you 'like butter'.
The light reflecting off the buttercup's shiny petals makes the yellow flowers stand out, but until now, the reason for the glow has remained a mystery.
Now, researchers have analysed the petals, and suggest that an extremely thin outer layer acts as an optical film to create the shine.
The light reflecting off the buttercup's shiny petals makes the yellow flowers stand out, but until now, the reason for the glow has remained a mystery
Researchers from the University of Groningen in the Netherlands discovered that the petals have an extremely thin outer layer - or epidermis - that measures just one-cell thick.
It contains a yellow pigment under which is an air chamber.
Dr Casper van der Kooi, who led the study, split the light coming from the petals into rainbow patterns called spectra.
He said: 'We discovered this layer acts as a thin optical film.
'The colour-generating mechanism is similar to oil on water or a soap bubble.
'Light is reflected on both sides of the epidermis where the cells and air meet.
'As the cell layer is very smooth and thin optical interference occurs and the reflected colours merge.
'This creates a white sheen which makes the petals seem glossy.'
This kind of thin pigmented film is unique in the world of plants.
Dr van der Kooi said: 'Butterflies use similar structures to produce colour - as do some birds - but buttercups are the only known flowers to do so.'
His team is the first to measure light spectra and conclude the cell layer acts as a thin film.
It's one of the classic games played in playgrounds around the world - putting a buttercup under your chin to determine whether or not you 'like butter' (stock image)
Dr van der Kooi said alongside the air chamber the petals have a starch layer which again scatters light and sends some of it back through the pigmented epidermis.
He said: 'Thus, the light reflected by the starch travels through the pigments twice, giving it a very rich yellow colour.'
He used a physical model of the petals which he had previously developed to explain how these unique anatomical features are responsible for both the intensity of colour and the sheen of the petals.
Dr van der Kooi, whose findings are published in the Journal of the Royal Society Interface, said the advantages are twofold.
He said: 'The first is under the right conditions the gloss reflecting from the epidermis can produce a bright flash visible to pollinating insects from a great distance.'
The sun needs to be high in a clear sky for this to happen.
The colour-generating mechanism seen in buttercups is similar to oil on water or a soap bubble. But this mechanism is unique in the plant world
The second is the buttercup is 'heliotropic' which means its flowers follow the sun - especially on cold days.
When it's cold the petals form a paraboloid-shaped cup - like a satellite dish - reflecting the sunlight towards the central area of the flower where the reproductive structures are located.
Dr van der Kooi said: 'We are still doing measurements but our hypothesis is this light helps to increase the temperature of the reproductive organs which enhances seed and pollen maturation.'
The researchers split the light coming from the petals into rainbow patterns called spectra. The team is the first to measure light spectra and conclude the cell layer acts as a thin film
Previous measurements by others have shown the centre of the flower can be several degrees warmer than the ambient temperature.
He said: 'But this may also be due to the shielding effect of the petals from the wind.'
This work has solved much of the mystery surrounding the buttercup.
Dr van der Kooi added: 'We can now explain the effects of the complex anatomy of the petals.'
Butterflies use similar structures to produce colour - as do some birds - but buttercups are the only known flowers to do so
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