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| Early frost Flowers - Mark Bower |
We are at the beginning of frost flower season although few botanists will ever see them. The "blooms" extrude around the lower stems of
Verbesina virginica on nights where the temperature drops well below freezing and they fade after a few minutes of direct sun or as the temperature reaches the mid thirties.
The delicate sheets of ice split the stem's epidermis lengthwise, thin enough that you can see your finger print through them. Early in the season they may extend 12 to 24 inches up from the base but as the winter rolls on they become shorter and eventually somewhat thicker. A hard freeze for several days which freezes the roots will end the season prematurely. Our personal record was 40 nightime blooms over a winter.
The mechanism of FF is the ability of water to "supercool," that is to drop below 32 degrees without crystallizing. This is what allows clouds to hold liquid water in the colder atmosphere. When
supercooled water is shaken or encounters a foreign particle it freezes rapidly, accounting for the icing on aircraft wings when they fly through cumulus clouds. This also accounts for the large accumulation of ice on trees and powerlines in ice storms that are so memorable to those of us in the Ozarks.
This is what happens when the supercooled water extrudes from a
V. virginica and contacts the outer stem's epidermis. You can see the dramatic ice crystalization of supercooled water in this demonstration on
Youtube.
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| Mark Bower |
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| FF asks a question - Mark Bower |
As frost flower season progresses the "blossoms" are lower to the ground and take on many extraordinary shapes. Stems may be damaged or horizontal but the ice marches on. Cups, curls and spirals are created, demonstrating nature's varied designs and sometimes a sense of humor.
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| White crownbeard - MDC |
This is the time of year to be watching for frost flowers along the weedy edges of fields and roadsides. These most commonly occur along the stems of
Verbesina virginica, a plant with small white flowers on 3-5 foot stems that are winged along the edges. It has a confusing list of common names including
frostweed, white crownbeard, iceplant, iceweed, and wing stem.
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| Frost flowers on dittany |
FF also can be found around the base of Cunila origanoides, whose common names include dittany, wild oregano, stone mint, and frost mint, and Pluchea camphorate. also known as stinkweed. These are smaller plants that are common in Missouri but less likely to cover a field edges.*
You can see some of the exquisite shapes that Mark Bower photographed before this last Friday's WOLF School field trip in this Flickr album.
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* Reports of FF on yellow crownbeard (Verbesina alternafolia) are probably due to confusion with Verbesina virginica as they frequently grow together and are hard to separate in winter time when the flowers are off. We have been monitoring tagged yellow crownbeard for years and have never seen FF on them.
The delicate sheets of ice split the stem's epidermis lengthwise, thin enough that you can see your finger print through them. Early in the season they may extend 12 to 24 inches up from the base but as the winter rolls on they become shorter and eventually somewhat thicker. A hard freeze for several days which freezes the roots will end the season prematurely. Our personal record was 40 nightime blooms over a winter.
The mechanism of FF is the ability of water to "supercool," that is to drop below 32 degrees without crystallizing. This is what allows clouds to hold liquid water in the colder atmosphere. When supercooled water is shaken or encounters a foreign particle it freezes rapidly, accounting for the icing on aircraft wings when they fly through cumulus clouds. This also accounts for the large accumulation of ice on trees and powerlines in ice storms that are so memorable to those of us in the Ozarks.
