Water causes the "Skeleton flower" to become transparent

In the heart of the Northern Hemisphere's woodlands, a unique and captivating flower blooms, known as the skeleton flower (Diphylleia grayi). Locals in northern Japan refer to it as sankayou, and this enigmatic plant has been a subject of scientific inquiry for decades.

This woodland perennial, found in the mountains of northern Japan, China, Russia's Sakhalin Island, and the Appalachian Mountains of the United States, is a member of the Berberidaceae family, which includes medicinal plants like mayapple and barberry.

The allure of the skeleton flower extends beyond its aesthetic and cultural appeal. Its unique biological properties make it a prime example of biomimicry, where observing and understanding a natural solution provides a blueprint for solving complex human engineering challenges.

One of the most intriguing aspects of the skeleton flower is its hydrochromic phenomenon – a change in appearance triggered by water. When wet, its petals turn transparent, displaying a structural colour caused by the way tissue scatters light. This optical trick is not just a visual spectacle; it has inspired researchers to replicate the effect in various applications, such as moisture-sensitive fabrics, energy-efficient smart windows, and energy-efficient architectural materials.

The transparency of the skeleton flower's petals is reversible, and they return to opaque white once dry. This reversible property has also been harnessed by scientists, who, in 2025, used the principle of refractive index matching to redesign the ELISA test, creating a "transparent ELISA" (tELISA) capable of detecting vanishingly small amounts of prostate-specific antigen. The tELISA reveals hidden traces of disease by letting light pass cleanly through its engineered fibers, potentially making it more sensitive than conventional tests.

This fascinating plant has also caught the attention of pharmacologists. Japanese botanist Yanagi Kimura conducted research in the 1960s on crude extracts of Diphylleia grayi, discovering significant anti-tumor effects. The active compounds in the skeleton flower's extracts were found to be similar in effect to, but more powerful than, podophyllin and colchicine, two well-known and potent plant-derived substances used in medicine.

However, despite its potential, the skeleton flower remains relatively unknown, and its long-term viability is a concern due to environmental pressures affecting similar specialist species. The plant has a specific habitat requirement and grows at a slow pace, making it vulnerable to environmental changes. Despite this, the skeleton flower, found in specific habitats worldwide, has not been formally assessed by the IUCN and does not have a conservation status.

In recent years, the scientific community has been delving deeper into the mysteries of the skeleton flower, uncovering its secrets and harnessing its unique properties for human benefit. As we continue to learn from this remarkable plant, it serves as a reminder of the wonders that lie hidden in the natural world, waiting to be discovered and utilised for the betterment of humanity.