When I was out east recently, I did a lot of hiking in the dense forests there, appreciating the diversity of the plants communities. The wildflowers were in full bloom, and I was particularly struck by the buttercups I saw.

The petals of the flowers were shiny, like they were wet—but they were not wet.

How, and why, do the buttercups have these shiny petals? This is a subject of current study, which is producing some answers.

The how is well understood—the petals have a thin layer of cells with an air layer beneath. This thin film creates a strong reflection. (Some insects use thinner films to produce bright colors, as discussed in another post, but this film reflects all colors.)

The why is a matter of debate, but two possibilities stand out. First, the shiny flowers might be more attractive to pollinators. Second, the shape of the flower, and the mirror-like reflection from the petals, means that sunlight reflected by the flower petals will fall on the stamens in the center of the flower, warming them. The warmer temperatures helps the stamens grow more quickly and produce more pollen, and there is some evidence that pollinators prefer warmer flowers. (There are some flowers that use energy to warm their flowers well above ambient temperatures.)

So, buttercups track the sun and use its energy to warm their centers. They aren’t just pretty; they are practical, serving as miniature solar collectors.