On damp days in the mountains of northern Japan, one of the most remarkable flower transformations unfolds. A patch of unassuming white flowers, that you’d barely notice against the forest’s deep green, suddenly become almost invisible. As rain settles on their petals, the blossoms of Diphylleia grayi—better known as the skeleton flower—turn from opaque white to crystal-clear. When the rain passes and the petals dry, the magic disappears, and they return to white once again.
For centuries, locals have known this woodland perennial as sankayou (サンカヨウ), admiring its fleeting transformation in much the same spirit as cherry blossoms. But in recent years, the skeleton flower has captured the attention of scientists as well.
A Flower of Flesh and Glass
At first glance, the skeleton flower looks remarkably unassuming. It grows knee-high, with broad umbrella-like leaves that carpet the cool understory of Japan, China, and Russia’s Sakhalin Island. In late spring, it sends up clusters of six-petaled white blossoms. By summer, those blossoms give way to striking stalks of cobalt-blue berries.
But rain is when the plant reveals its secret. The petals don’t contain any pigment to make them white. Instead, their whiteness is structural—caused by the way their tissue scatters light. Peacock feathers and some butterflies also have structural color, generated by how microscopic structures bend, scatter, or interfere with light. Unlike chemical pigments, structural colors can shimmer, shift, or even vanish depending on the angle or environment. That’s what happens when the flower gets wet.
When dry, the petals are filled with air pockets. Light bounces chaotically through these spaces, reflecting back as white, the same principle that makes snow appear bright. As soon as water fills those microscopic gaps, the trick collapses. Water and plant tissue bend light in almost the same way, so the scattering stops. Light passes straight through, leaving the petals transparent, save for the tougher veins that remain visible.
The effect is entirely reversible. Once the petals dry, air returns, scattering light again, and the flowers reclaim their opaque whiteness. Scientists call this phenomenon hydrochromism—a change in appearance triggered by water.
It’s not clear why the plant evolved this peculiar mechanism. Some scientists suggest the transparency may help the blooms stand out to pollinators on dark, rainy days. Others think the trait may simply be a side effect of the petal’s delicate structure, with no clear purpose at all.
A Survivor From Another Age
The plant’s history is also rather unusual.
The skeleton flower belongs to the barberry family, Berberidaceae, which includes medicinal plants like mayapple and barberry. Botanists believe its current distribution—East Asia and the distant Appalachian Mountains of the United States—reflects an ancient forest that once spanned the Northern Hemisphere. As glaciers advanced and retreated, those forests fragmented, leaving relict species like Diphylleia stranded in scattered mountain refuges.
Its slow-growing underground rhizomes can persist for decades, spreading into small colonies beneath the canopy. Each spring, the cycle repeats: broad leaves unfurl, flowers bloom and turn ghostly in the rain, berries ripen to feed wildlife, and by autumn, the plant retreats underground to endure the cold.
It’s perhaps ironic that in Japan, the skeleton flower has become entwined with cultural traditions that celebrate transience. Locals associate it with impermanence, linking it with the concept of mono no aware, the awareness that all things are fleeting. But although its color may be impermanent, the flower itself is remarkably resilient.
The skeleton flower has become a symbol for this metaphor. Tattoo artists use the flower as a symbol of resilience, authenticity, and personal transformation. Photographs of its glassy petals regularly go viral online, where they are celebrated as proof that nature still holds surprises unseen by most of us.
For all its symbolism, however, the skeleton flower remains, at heart, a survivor of ancient forests—an unassuming perennial whose greatest beauty is revealed only in the rain.
From Forest Floor to Future Technology
Scientists are also interested in this flower, for remarkably diverse reasons.
In the 1960s, Japanese botanist Yanagi Kimura conducted research on crude extracts of Diphylleia grayi. His findings were remarkable: the extracts demonstrated significant anti-tumor effects on transplantable animal tumors. He noted that the active compounds were similar in effect to, but more powerful than, podophyllin and colchicine, two well-known and potent plant-derived substances used in medicine. This early research highlighted the plant’s potential as a source of novel bioactive compounds, though this was not further explored.
Other researchers have replicated its optical trick by engineering porous films from silicone polymers. Dry, the air-filled pores scatter light, turning the material opaque. Wet, the pores fill with water, making it transparent. These hydrochromic films could inspire everything from moisture-sensitive fabrics to energy-efficient smart windows that shift from translucent to clear without electricity. The same principle is being applied to create energy-efficient architectural materials. Smart windows based on the skeleton flower’s mechanism could switch from a light-scattering, translucent state (providing privacy and reducing solar heat gain) to a fully transparent state in response to humidity or a direct application of water. This offers a low-energy, passive method for controlling light and heat transmission in buildings.
In 2025, a team of Chinese researchers borrowed its principle of refractive index matching (the same physics that makes petals turn transparent in rain) to redesign a classic diagnostic tool for cancer: the ELISA test. By building nanofiber membranes that become optically clear when wet, they created a “transparent ELISA” (tELISA) capable of detecting vanishingly small amounts of prostate-specific antigen, a key cancer marker, at concentrations thirty times lower than conventional tests. Just as the skeleton flower reveals hidden veins when water fills its tissues, the tELISA reveals hidden traces of disease by letting light pass cleanly through its engineered fibers.
For one flower that’s relatively unknown, that’s quite the scientific performance.
A Remarkable Plant Under Threat
Diphylleia grayi has not been formally assessed by the IUCN and doesn’t have a conservation status. Its official conservation status is therefore “Not Evaluated” (NE). But this does not mean the species is secure; it simply means that a comprehensive global assessment of its population size, trends, and threats has not yet been undertaken and submitted for inclusion on the Red List.
The skeleton flower has very specific habitat requirements. In fact, it’s found in only three habitats in the world. Its slow growth and propagation also make it more vulnerable in the face of changing habitats. While not officially listed as threatened, there are very real concerns for the long-term viability of Diphylleia grayi based on the environmental pressures that affect similar specialist species.
It would be a shame for such a remarkable flower to face its demise.
The allure of the skeleton flower extends far beyond its aesthetic and cultural appeal. Its unique biological properties have made it a subject of scientific inquiry for decades, first in pharmacology and more recently as a source of inspiration for cutting-edge materials science. Diphylleia grayi serves as a prime example of biomimicry, where observing and understanding a natural solution provides a blueprint for solving complex human engineering challenges.
