Buttercup flowers are known for their intense, shiny yellow color. For over a century, biologists have sought to understand why the buttercup stands out. University of Groningen scientists have now brought together all that was known about the buttercup and added some new information too. The results will be published by the Journal of the Royal Society Interface on February 22, 2017. The article will be titled “Functional Optics of Glossy Buttercup Flowers.” The anatomy of the buttercup's petals is the first step in discovering the secret of its color. The petals have a one-cell thick epidermis, which contains a yellow pigment. Underneath this very thin cell layer is an air chamber. During his work as a Ph.D. student at the University of Groningen, Dr. Casper van der Kooi (who now works at Lausanne University, Switzerland) measured light spectra reflecting from this epidermal layer. “We discovered that this layer acts as a thin optical film. The color-generating mechanism is similar to oil on water or a soap bubble,” says Dr. Van der Kooi. “Light is reflected on both sides of the epidermis, where the cells and air meet. As the cell layer is very smooth and thin, optical interference occurs and the reflected colors merge. This creates a white sheen, which makes the petals seem glossy.” This kind of thin pigmented film is unique in the world of plants. “Butterflies use similar structures to produce color, as do some birds, but buttercups are the only known flowers to do so,” says Dr. Van der Kooi. The structure of the epidermis has been described before, but Dr. Van der Kooi and colleagues are the first to measure light spectra and conclude that the cell layer acts as a thin film.
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