Lichen is actually a symbiotic relationship between algae and fungus. The fungus provides structure and protection for the algae, which in turn creates food the fungi (and itself) through photosynthesis. Lichen come in several basic shapes: crustose, which hug the host surface; foliose, which appear to be layers; and fruticose, which look like little plants. Lichen's color is usually from the fungus body, but in the case of greenish-grey lichen, a combination of the fungus and chlorophyll provide the hue (humans have used lichen as a source of dye). Lichen are found just about everywhere, from the poles to the tropics, from dry, high mountains to deep, damp valleys.
Erosion is one of lichen's best skills. The fungus secretes acids that carve into the host rock to provide a better grip, and this also converts rock into soil (over a long period of time).
The Spanish moss that hangs from trees in the U.S. -- most famously in the Southern states -- is actually a lichen (Tillandsia usneoides), not a moss. Mosses are 100% plant. Speaking of moss, I'm reminded of a Simpsons episode (Das Bus) where the children are trapped on an island that turns into their own version of Lord of the Flies. At the end, Lisa finds how the pigs were able to survive on the island: by eating the moss that grew on rocks. Perhaps it was actually lichen, and the giant team of fact checkers didn't catch the mistake. In the Arctic, lichen are an important food source for many kinds of animals.
Some of the lichen patterns remind me of the paintings of Clyfford Still, one of the Abstract Expressionists. Take a look at 1948-C or 1950-A No. 2 in the Hirshhorn Museum on-line collection and see if you agree.
Below are some photos of lichen I took on the hike and a few that I shot near the Columbia River Highway in Oregon.
Lichen-covered tree branches
Two colors of crustose lichen on a boulder
A foliose lichen on a boulder
Grey and yellow foliose lichen on a boulder
Lichen and moss on a tree trunk, near the historic Columbia River Highway in Oregon
Chrysothrix candelaris lichen on a cliff face near Multnomah Falls, Oregon
(I know the species name because there was a sign nearby, not because of any lichen-identification skills)
Random link from the archive: Another Flourless Dessert: Torta Regina
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