From a distance it looked like a white plastic bag that had been snagged on the dead stem of a weed. On closer inspection, it turned out to be a Frostweed (Verbesina virginica), with an ice sculpture wrapped around its stem. Frostweeds earn their name in cold winters, when moist soil and a hard freeze combine to create the conditions for these plants to produce (passively) interesting and beautiful ice sculptures like the one pictured below. For more detailed information on Frostweeds, see last years article : https://bwwellsassociation.wordpress.com/2016/01/27/frostweed-verbesina-virginica-blooms-in-central-north-carolina/.
The formation of Frostweed ice sculptures usually occurs at the base of the plants. In this case, the large stem was preserved structurally intact, and the ice was able to climb four feet up the six foot stem, an unusual happening.
Below is a closer look at the ice pattern at the base of the plant. An indistinct groove can be seen in the center, where the stem is located.
The two photos that follow illustrate the complex patterns formed when the cold sap turns to ice and either extrudes from or is formed at the surface of the stem.
The picture below illustrates how the force of the expanding ice splits the stem open in the area near the top of the plant.
Although the ice in these sculptures looks thick and robust, it is actually thin and fragile, adding very little to the weight of the plant. This plant stayed upright during windy mornings in spite of the shell of ice, and hosted a number of large, repeat blooms. The ice melts very quickly in sunny conditions.