Made of thin ribbons of ice that extend into intricate patterns when frozen water breaks through the slits of certain types of plant stems, these icy blooms, which only appear for hours at a time, can break with a single touch.

They are usually found in the Eastern half of the US, especially in the upper half where hard freezes are more common and often resemble clouds of cotton candy or spun glass.

It’s become a well-known phenomenon, indicating the arrival of winter and people rush out of bed to get a glimpse of them, before the sun melts them away.

“You have to be at the right time, at the right place,” said Alan Templeton, professor emeritus at Washington University in St. Louis, Missouri, who does a lot of conservation genetics. “You see them and you know they’re going to be gone in an hour or two. So it’s this very ephemeral, but highly variable beauty, and it’s that combination that makes me so fascinated by them.”

While the intricate ice patterns are found near the base of a few common plants, including white and yellow wingstem plants, Templeton explained that the conditions need to be just right for them to appear. And once they do, they won’t be back for another year.

The ground has to be warm and wet enough for water to travel up from the plant’s roots into the stem, while the air needs to be cold enough to freeze the liquid so that it breaks through the stem, creating the flower-like appearance.

Templeton said he first came across frost flowers decades ago while scoping out an area in the Missouri Ozarks for field work.

“They’re really beautiful,” he said. “And also each one is unique. There’s no two frost flowers that are the same.”