thermonasty, home

The cold weather continues, and a sign of the times, besides the skim ice and waterfall icicles, is an event we call the "rolling of the ferns." Now, a few posts ago, I wrote about how, among the sensitive fern species, below-freezing temperatures simply give the fronds terminal frostbite and leave the foliage shriveled and very, very dead. But some ferns, the Rock Polypody among them, are evergreen and have adapted to icy insults. One important strategy in these hardy plants is a practice that botanists term "thermonasty." This sounds unpleasant, but it's simply shorthand for the way ferns roll their leaves when the going gets frigid to minimize surface area and the possibility of frost damage. The Polypody on the local boulders were thermonastying when I walked by this morning. The strategy worked. By the time the temperature got into the 40s this afternoon, I noticed that the leaves were back to normal, none the worse for the experience.