When they examined P. condensata on a cellular level (above), they realized that the fruit produces its characteristic color through structural coloration, a radically different phenomenon that is well-documented in the animal kingdom but virtually unknown in plants. They determined that the fruit’s tissue is more intensely colored than any previously studied biological tissue—reflecting 30 percent of light, as compared to a silver mirror, making it more intense than even the renowned color of a Morpho butterfly’s wings. Their findings were revealed in a 2012 study published in the Proceedings of the National Academy of Sciences.
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. Here’s a view of the fruit through an electron microscope, revealing the presence of the color on a cellular level.
Experimenting with different ways to look at the fruit, the researchers studying Viburnum tinus used a transmission electron microscope to get a side view of the plant’s cells. The cell’s nucleus was indeed larded with blobs of pigment. But between it and the surface of the skin there was an enormous object, as thick as the nucleus itself. A closer look revealed that it was made of neatly spaced layers.