By Emily Underwood
Don't let the iridescent blue of this tiny African fruit fool you: It's neither tasty nor nourishing and contains no pigments to extract. Instead, the vivid sparkle of Pollia condensata comes from the interaction of light with the fruit's skin, which contains layers of microscopic, rod-shaped fibers of cellulose. Stacked like spiral staircases, the rods in the fruit's epidermal cells are spaced at slightly different intervals. Depending on the distance between the rods, the spirals reflect different colors. Most reflect blue light, but others reflect different parts of the visible spectrum, producing a pixelated rainbow. The overall effect is a metallic blue brighter than any yet described in a biological material, researchers report online today in the Proceedings of the National Academy of Sciences. While animals like butterflies and peacocks produce iridescent color using layers of chitin, iridescence is almost unheard-of in plants. The fact that P. condensata produces rainbows of color by layering cellulose in sophisticated patterns is an exciting example of convergent evolution between plants and animals, says biologist Beverley Glover at the University of Cambridge in the United Kingdom. The fruit's coloration may have evolved to capitalize on birds' attraction to sparkly objects, she speculates, or to trick them into eating something that looks like a blueberry without going to the trouble of actually making juicy flesh.
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