Art, spring flowers, and the discovery of a blue halo

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I have a sketch book, or as it was marketed, a visual journal. I think I prefer the name visual journal – each picture was something I chose to draw, not something that was put in front of me as in art class, and each picture has an added dimension of having a memory attached to it. And, as it turns out, sometimes a picture will end up having some form of scientific relevance too, as happened with my picture of spring flowers.

Spring Flowers

My picture of Ursinia speciosa, commonly known as Namaqua-ursinia

On a beautiful spring evening, I stumbled upon a bloom of bright orange and yellow flowers which intrigued with their very circular structure, and delighted with their bright, cheerful colouring. I liked them so much I decided to draw them. Known as Ursinia speciosa, these flowers have a circle around the middle that is so black that it’s almost blue. I didn’t realise it at the time, but a couple of weeks ago when a paper was published in Nature about a blue halo on flower petals, it became clear that a light scattering mechanism was causing the “almost blue” effect.

Bees are attracted to plants that have blue or violet flowers, but these shades are difficult to produce in nature since particular genetic and biochemical elements are required. And so many plants have evolved a different mechanism of producing blue or violet hues. Tiny, disorded structures similar to dried spaghetti occur on the surface of plant petals and, by scattering light, they produce a “blue halo” of blue and UV light which attracts bees to the flower.

Humans can only see this effect on darker petals, such as the black band on these Ursinia flowers, but bees are much more sensitive to this colour range. “Unlike us, bees have enhanced photoreceptor activity in the blue-UV parts of the spectrum,” explains Edwige Moyroud, the study’s lead author. “We can’t distinguish between a yellow flower with a blue halo and one without – but our study found that bumblebees can.”

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