I looked out in my backyard this morning, December 7, and once again, as has been the case for the first hard freezes since the end of November and first of December, we had our first “frost flowers” of the year. These ephemeral beauties are produced by two plant species in the Ozarks, and worldwide, by 30 plant species.
One Ozark native that produces frost flowers is white crownbeard or Virginia frostweed (Verbesina virginica), an otherwise non-descript, late-blooming member of the aster family, 2-4 feet tall with ragged white flowers in flat-topped clusters.
Another plant found in acid woodlands, American dittany (Cunila origanoides), which grows in dry, wooded habitats, also produces frost flowers. A small, wiry plant about a foot tall, it has small clusters of purple-bluish small flowers in whorls in the leaf axils. This year we had a perfect set-up for frost flowers with a good rain the week before the first frost.
Pennsylvania physician, William Darlington (1782-1863) seems to be the first to record observation of frost flowers in American dittany, or as he called it, Maryland Cunila. In the second edition (1837) of his Flora Cestrica (an herborizing companion for the young botanists of Chester County, Pennsylvania) he writes, “In the beginning of winter, after a rain, very curious and fantastic ribbands [sic.] of ice may often be observed, attached to the base of the stems of this plant—produced, I presume, by the moisture from the earth rising in the dead stems by capillary attraction, and then being gradually forced out horizontally, through a slit, by the process of freezing. The same phenomenon has been noticed in other plants.”
This phenomenon has been deemed “crystallofolia.” It usually occurs only during the first few frosts of the year.
For me it has become a tradition to search for the first frost flowers. I keep my camera equipment outdoors the night before I know we’re going to get our first hard freeze so the lens won’t fog up when I take it from the warmth of the house to the outdoors. It’s one of my favorite photographic subjects in cold weather.
Bob Harm at the University of Texas Austin has developed web pages with the most complete information on the subject. See details on the subject at the Flora of Texas website, biosci.utexas.edu.