The Nature of Eureka: Happy Crystallofolia Season

906

By Steven Foster – It is crystallofolia time! Perhaps new to your natural history vocabulary, “crystallofolia” is a term coined by Bob Harms of the Plant Resource Center, University of Texas, Austin, who for many years has been investigating the phenomena we commonly call “frost flowers” – those beautiful ice formations produced at the base of only two native plant species in the Ozarks.

Anyone who has driven along streets at the edge of town on a cold frosty morning has likely noticed them. Our two native plant species that exhibit this phenomenon are American dittany (Cunila origanoides) and white crownbeard or frostweed (Verbesina virginica) both late-blooming wildflowers you may not notice except at this time of year. Their frost flowers or twisted ribbons of ice appear for a few days (up to a couple of weeks) after the first hard freezes in autumn. These ephemeral sculptural beauties of ice appear at the base of the plant. The delicate, elegant ice formations emerge laterally from the stem, just above the ground in the case of American Dittany, but from ground level to two feet up the stem in the case of white crownbeard.

Why does this phenomenon only occur in a select few plant species instead of all plants? Speculation is that a combination of characteristics unique to the plant in combination with the external physical forces provides a perfect opportunity for the frost flowers to develop. The xylem, vascular tissue within plants that helps conducts water upward in the stem, is probably quite firm, with secondary rays at a right angle that is strong enough to conduct water during a frost event but its tensile strength reaches a point during the first cold frosts that freezing water burst through the epidermis at a right angle to the stem. As it does so, it ever so slowly punches moisture into the freezing air extruding ribbons of ice that we call frost flowers. Botanists have written about and speculated on the phenomena associated with frost flowers for 200 years.

Early morning walks by people with a smart phone camera in their pocket has created a crowd populated social media collection of frost flower images in the parts of the country where these plant species grow. They are an amazing sight to see and ponder at this time of year, reminding us of the ephemeral beauty to be found in nature. For the most complete information on the subject, see the detailed article on the subject by Bob Harms at the Flora of Texas website: w3.biosci.utexas.edu/prc/VEVI3/crystallofolia.html.