Berry Brillant: Indigo Fruit Lacks Blue Pigment
Although a vibrant blue, this African fruit contains no blue pigment, according to new research by Silvia Vignolini and her colleagues at the University of Cambridge. The jewellike berry is from the plant Pollia condensata, which grows across Africa. Each plant produces up to 40 shiny bits of fruit. The blue and its beautiful iridescent shine are caused by a Bragg reflection—intense peaks of light generated at certain wavelengths and angles—created by spirally stacked cellulose fibers that form multiple layers in the fruit's skin. "The reflected color differs from [skin] cell to cell, as the layer thicknesses in the multilayer stack vary, giving the fruit a striking pixelated or pointillist appearance," Vignolini wrote in a paper published in the September 10 Proceedings of the National Academy of Sciences. The researchers note that the berry's coloration is more intense than any biological material studied to date.