The beauty of lichens . . . How they flourish! I sympathize with their growth.
H. D. Thoreau
There’s a lot to like about lichens. Found in wild and urban places, from the arctic to the tropics, in deserts and on mountaintops, affixed to buildings and 
monuments, they are tenacious organisms unlike any other. Even on my quarter acre house-lot I come across lichens on tree trunks, the stone foundation of my home, brick walkways, fences, and the old cedar shake roof of my woodshed. Under our feet, out of sight, often fading to background, they can serve as reminders of remarkable and subtle natural forces all around us. They create mosaics of incidental and accidental beauty where least expected.
Combinations of funguses and green algae or cyanobacteria (blue-green algae), lichens are the essence of symbiotic cooperation. The fungus encloses the algae and supplies water, organics, and minerals from its surroundings, while the algae manufacture carbohydrates by photosynthesis. This self-reliant relationship withstands extreme temperature changes and can completely dry out without dying.
You needn’t know the names of various lichen species to appreciate them. Generally classified in three categories, they are crusty and two-dimensional, leaflike, or shrubby with lots of fine branching structures (like reindeer (moss) lichen). They grow incredibly slowly, up to half an inch a year and often much less. Though they get little respect for it, lichens are among the oldest living things on earth. Some are 5,000 or more years old.
The ultimate in unsung pioneers, lichens colonize the harshest environments on earth. They are first in barren landscapes where plants cannot grow, and in places denuded by disaster. On journeys 
in Labrador, I’ve found entire landscapes plushly carpeted with lichen. They prepare a way for other vegetation by breaking down bare rock and creating soil through secretion of certain chemicals and by their mere attachment to stone. When my son was young, we climbed to the summit of New Hampshire’s Mt. Jefferson where he picked up a rock pocked with map lichen—flat discs of pointillist yellowish-green crust outlined in black. In response to his question, I gave a quick tutorial. It took repeated assurances to convince him that the lichen would not “eat” his rock before he could show it to his mom back home. Lichen time is on a scale beyond our understanding.
Lichens are a source of nesting material and food for mammals and birds, especially in the far north where, for example, reindeer lichen is eaten by caribou. 
They are also in the diets of some peoples, have been used to produce medicines, and to dye products as diverse as Harris tweeds and litmus paper. Shrubby lichens have been used to imitate trees and bushes for model railroads and in architectural models.
A kind of natural hieroglyphic, lichens tell stories to scientists who can read their language. Lichenometry estimates the age of exposed rock surfaces by lichen growth rates. With their sensitivity and tendency to accumulate certain pollutants, lichens have been used as biomonitors of air quality. Thriving in clean atmospheres, the biggest threat to their survival is not predation, but dirty air.
Beautiful not just for their ecological functions, lichens are a visual and tactile delight that can be 
seen in any season. They come in a startling array of hues from subtle black, green, and gray to vibrant shades of orange, yellow, red and green. Shapes, patterns and textures vary even more. Flat crusty lichen may grow in irregular concentric bands and starbursts, with warty or grainy surfaces, and in almost cartographic designs. Leaflike types form rosettes, discs, ovals, or jagged and wrinkled lobes. Shrubby lichens produce tufts or patches with fine stalks or branching structures, sometimes with curling, hair-like filaments. I like to gently touch their rough, but delicate surfaces and let them tickle my hands.
Some of the best places to look at lichens are not in natural areas, but among human works. They tattoo many traditional stone walls here in New England. In cemeteries, they form an ersatz graffiti on many memorials, leaving some completely obscured. Lichens may grow ever so slowly, but they will seem to have appeared overnight on masonry structures, trees, and rocks once you start looking. Afterward, the rest of the world will never look the same.
