Here’s yet another item to add to your list of “Phenomenons of Nature That Seem Too Extraordinary to Be Real.”
Pollia condensata, sometimes called marble berry, is a wild plant that grows in forests throughout Ethiopia, Ghana, and other areas in western Africa. It’s not edible, it can’t be made into a drinks, and its leaves are ordinary. It would be wholly unremarkable if it weren’t for one thing: its tiny fruits.
The fruits of P. condensata are a glimmering, iridescent blue color, often metallic or pixelated in appearance. Even more impressively, they retain the same vivid color for years—or decades. (One specimen from 1974 still has the same brilliance!) They have been used decoratively for a long time in local communities, but it’s only now that scientists are unraveling the mystery of how they produce their bright, long-lasting color.
In a study published in the Proceedings of the National Academy of Sciences, a team of researchers from the Kew Botanical Gardens, the University of Cambridge, and the Smithsonian Natural History Museum attempted to discover just where this berry’s vivid color comes from. They began by attempting to extract a color pigment from the berry, but to their surprise, they discovered that the berry has no pigment.
Instead, they determined that the fruit’s color comes from a phenomenon known as structural coloration, the same mechanism that supports the color of peacock tailfeathers (which are actually pigmented brown) and blue Morpho butterfly wings. While structural coloration is well-known in animals, it has barely ever been documented in plants. Smithsonian describes how it works:
“The vast majority of colors in the biological world are produced by pigments—compounds produced by a living organism that selectively absorb certain wavelengths of light, so that they appear to be the color of whichever wavelengths they reflect. For example, most plants are green because of the pigment chlorophyll, used in photosynthesis, which absorbs most wavelengths of visible light except green, reflecting that color into our eyes. As a consequence, plant colors created by pigmentation appear to be the exact same hue no matter which angle we view them from, and the color degrades when the plant dies.
P. condensata, however, produces its vibrant blue via tiny, nanoscale-size cellulose strands that are stacked inside its skin. These strands are arranged in layers of twisting, arced helix shapes, which interact with each other to scatter light and produce the fruit’s deep blue coloration.”
The researchers found that P. condensata‘s tissues are more intense in color than any other biological tissue that has yet been studied. They reflect 30 percent of the light that hits them, similar to a silver mirror. The stacked nanoscale fiber construction lends the berries an additional color quirk: the individual skin cells appear to change color, depending on what angle you’re looking at them from, as the light hits the surface in many different ways.
Click through to see two more photos of this awe-inspiring plant!
A bunch of fresh berries, growing wild:
Photo Credit: PNAS
The amazing nanoscale structures of the plant, as seen through an electron microscope:
Photo Credit: PNAS