by Bob Harms ()

Pluchea odorata (Marsh Fleabane) Crystallofolia

P. odorata, December 25, 26°, N. Hays County, Texas
Both true frost (left side) and crystallofolia (‘frost flower’) formations (right) shown.

Crystallofolia (‘frost flowers’) are not generally known to occur with our Central Texas marsh fleabane. But the phenomenon is not exclusively associated with our frostweed (Verbesina virginica). And the formations are no less picturesque. (John Le Conte studied the phenomenon with a closely related species, Pluchea camphorata, in Georgia in the late 1840s, but to my knowledge its occurrence with Pluchea odorata has not been reported.) When I visited the area on Dec. 16, a day with many Verbesina virginica crystallofolia, this species had none. I was thus surprised to find them on December 25 (there had been only a trace of rain in the interval). The same plants were seen to produce new formations on Dec. 29, Jan. 1, Jan. 13 and Jan. 20 (and presumably with serveral other hard frosts in between, being smaller with each repetition).

S. creek, Jan 10 S. creek PLOD detail, Jan 10
10 January 2010, c. 12° F
In 2009 our area had both P. camphorata and P. odorata. Because of a record drought P. odorata was restricted to a dry creekbed and didn't develop until after September rains, and with the end of the drought most plants were either under water or at water's edge (where the flowing water kept temperatures too high for crystallofolia). Nonetheless, with record low temperatures (c. 12° F), Jan. 8–10, a few plants managed to produce frost formations — but P. camphorata, which was in drier areas, did not.

[Most images below can be enlarged by clicking.]

New ice on December 29, 2007 Yet more ice on January 1, 2008
Above plant with ruptured epidermis after freeze of December 25, 2007. New ice (much reduced) Jan. 13.

Woody secondary xylem splitting as a result of exposure
to actual freezing, Dec. 29.

Repeat performance on Jan. 1.

Much smaller on Jan. 13.

Additional marsh fleabane ice formation pictures taken December 25, 2007.
Click on image to view an enlargement.