Most plants get their coloration from pigments, but an endangered South African cycad gets its unique silvery-blue hue from wax crystals and an underlying chlorophyll-rich layer, according to a recent study. Researchers say understanding how such layers work could pave the way for creating materials that protect from UV and water exposure.

Cycads, sometimes described as “living fossils,” are an ancient group of cone-producing plants that appeared around 270 million years ago, predating even the dinosaurs.

The study examined the “remarkably glaucous” or bluish leaves of Encephalartos horridus, the Eastern Cape blue cycad. The species is native to shrubland and rocky areas of South Africa. It’s listed as endangered due to declining subpopulations and poaching.

The study explained that land plants are typically coated with a water-repelling layer called a cuticle, which protects plants from environmental stresses. Cuticular wax comes in two types: intracuticular wax found inside, and epicuticular wax (EW), found outside the cuticle. The genus Encephalartos, which includes cycads,diverged around 9 million years ago and evolved to have substantial layers of EW.

“To the best of our knowledge, visually detectable EW deposits have been primarily documented in angiosperms [flowering plants] and are largely absent in other major plant lineages,” the researchers wrote. “Thus, studying the unique properties of an extant gymnosperm species such as E. horridus may provide valuable insights into plant adaptations to challenging environments.”

Researchers learned that the cycad’s EW is mostly composed of a wax compound that forms tubular crystals that reflect light from ultraviolet to blue wavelengths, resulting in the bluish sheen.

The study noted that the wax is common in gymnosperms — the group of plants that produce uncovered seeds, including cycads — and has even been found in ginkgo fossil records dating back 300 million years. This suggests the ability of plants to produce this wax compound “emerged early in land plant evolution.” But only a few species can use it to produce color.

“The leaf surface is coated with ultra-thin wax crystals about one ten-thousandth of a millimeter wide,” Takashi Nobusawa, study co-author and assistant professor at Hiroshima University’s Graduate School of Integrated Sciences for Life, said in a press release. “Peeling off the leaf’s surface layer makes the blue disappear. But placing it back on a dark surface [rich in chlorophyll] brings the blue back, as if by magic.”

Nobusawa added in an email to Mongabay that, “The study is fascinating because it shows how an evolutionarily ancient plant lipid can self-assemble into crystals that both change color and add protective functions.”

He said that understanding the process to create such a wax compound “could open the way to bio-based coatings that are reflective, UV-protective, and water-repellent — for example, a sustainable alternative to car wax.”

Banner image of an Encephalartos horridus in a greenhouse under natural sunlight. Image courtesy of Takashi Nobusawa/Hiroshima University.