But once the flowers of the Viburnum tinus plant fade, the shrub makes something unusual: shiny, brilliantly blue fruit.

But researchers reported last week in Current Biology that viburnum’s blue is actually created by layers of molecules arranged under the surface of the skin, a form of what scientists call structural color.

Rox Middleton, a researcher at University of Bristol in England and an author of the new paper, had been studying the African pollia plant, which produces its own exotic blue fruit.

But viburnum fruit were everywhere, and she realized that their blue had not been well-studied.

The pollia fruit’s blue is a form of structural color, in which light bounces off a regularly spaced arrangement of tiny structures such that certain wavelengths, usually those that look blue or green to us, are reflected back at the viewer.

In pollia fruit, the color comes from light interacting with thin sheets of cellulose packed together.

Mathematical models of the layers showed that this bumpiness helped provide the particular cloudy blue of the viburnum fruit.

In terms of blue fruits with unusual coloration strategies, viburnum has certainly been easier to get ahold of than the pollia fruit, Dr