With good rains in October and early November, followed by the first hard freeze dipping into the teens or low twenties on the morning of November 10, it created the perfect opportunity for the formation of a phenomena known as “frost flowers.” It also called “crystallofolia,” a term coined by Bob Harms of the Plant Resource Center, University of Texas – Austin, who for many years has been investigating the phenomena.
Frost flowers are ice formations at the base of certain plant species that occur mostly at the earliest frost of the fall, especially for a relatively non-descript, late blooming wildflower called white crownbeard or frostweed (Vernonia virginica) and American dittany (Cunila origanoides) which is a small wiry mint family member which has bluish-violet flowers late in the summer. It mostly occurs in acidic woodlands, and often produces frost flowers later in the fall, extending into the winter months if conditions are right.
There were hundreds of frost flowers from white crownbeard visible in Eureka Springs on ice-cold mornings during the last couple of weeks. Of course, you had to bundle-up and get out to view them before the temperatures rose above freezing or a bright sun melted them. Frost flowers are truly ephemeral.
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, provide 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 are strong enough to conduct water during a frost event.
However, its tensile strength reaches a point at which freezing (therefore, expanding) water bursts through the epidermis at a right angle to the stem. As it does so, it ever so slowly pushes moisture into the freezing air, extruding the ribbons of ice that we call frost flowers. Botanists have written about and speculated on the phenomena for more than 200 years.
For the most complete information on the subject, see the detailed article by Bob Harms at the Flora of Texas website: w3.biosci.utexas.edu/prc/VEVI3/crystallofolia.html.