Researchers from the University of Cambridge have discovered that certain flowering plants have tiny ridges on their petals that scatter light and cast a blueish hue over their blooms.
Human eyes are not trained to pick up that strange glow, but it is extremely visible to bees. As a result, the scattering is likely a way for plants to attract pollinators.
“The exciting thing is that it is a new optical trick – we didn’t know that flowers could use disorder to generate a specific colour, and that is quite clever,” said study co-author Beverley Glover, a professor at the University of Cambridge, according to The Guardian.
The team began this research when they discovered that tiny ridges on the petals of certain plants could bend light and give them a special sheen. They then followed up on that finding by seeing if it occurred in other species with big, flat petals.
To do that, scientists used a range of microscopy techniques to look at 12 different flowering plants and note how they diffracted light. This revealed that the architecture of the nanostructures differed from species to species. Some had different spacing on their ridges, while others had ones that were different heights.
However, despite the small variations, all of the flowers had a weak iridescent sheen. In addition, the ridges also scattered both blue and ultraviolet light to create what researchers call a “blue halo.” That feature appears different in each species, depending on how much height and space exist between a flower’s ridges.
To see the affect of the halo on pollinators, the team released bumblebees on a series of small squares that had different colored pigments and surface structures. Some had a smooth surface, some had ridges that gave them an iridescent sheen, while others had ridges that produced a blue halo. Then, once the bees landed on the squares they were given a either a sweet or bitter solution.
Data shows that the insects could learn which squares to visit for a tasty treat even if the shapes were moved around throughout the study. That suggests bees are able to see optical effects generated by the surface texture. They can also spot a blue halo that does not have an iridescent sheen.
These new findings shed light on flowering plants and give scientists a new glimpse into plant evolution. They hope further study of the topic could help them better understand the connection between pollinators and plants.
“We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life – that flowers couldn’t do any better,” added glover. “”It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively.”
The results are published in the journal Nature.