Gorgeous and rare
I had never heard of frost flowers until a few days ago, when someone sent me a link to this page explaining all about them. How can I have not known about something so amazingly beautiful?
Frost flowers (scientifically known as crystallofolia) are as ephemeral as they are breathtaking. Imagine something as delicate as one giant snowflake, and you're close. Frost flowers form under very specific conditions: the ground has to be warm enough for plants to not be dormant, and yet the air must be cold enough for frost to form. It's a difficult balance, and it means that most people will go their entire lives without seeing a frost flower in person.
The physics of frost flower formation are intricate. Active (i.e. non-dormant-for-winter) plants are constantly sucking water up from the ground through their stems. If the plant has not gone dormant when the air falls below freezing, the sap in its veins can freeze. When sap freezes, it expands. When this happens, it bursts the cells and stems of the plant and creates microscopic cracks.
Under a particular set of conditions, the plant continues to draw water up into its stem after it has been cracked by ice formation. The water flows out of the microscopic cracks and freezes as it hits the air. More water is drawn up the stem, flows out of the cracks pushing the previously-frozen stuff forward, and freezes itself.
This essentially creates a situation where frost is being extruded from the leaf or stem of a plant. The shapes that it forms are called "frost flowers," and they are as amazing and as unique as snowflakes. Some of them look like puffy clouds of cotton candy; others like small trumpets made of ice, and still others form bizarre curlicues and rams' horns.
If you find one, the Kuriositas site recommends that you do not try to touch it. They are so fragile that they break at the slightest touch, and melt from the warmth of your fingertips. Instead, take a picture - and take it fast, because frost flowers dissolve quickly as the sun hits them or the day warms up.
There is another kind of phenomena called "frost flowers" which grow on newly-formed sea ice. Although these two phenomena have nothing in common but their name and the fact that they are formed by freezing water, the sea ice frost flowers are gorgeous as well.