Lichen represents symbiotic relationship

What a great season for a hike!

Yes, it might be cold, but it's a chance to bundle up in boots, a warm sweater, windbreaker and gloves, and with something snuggly and toasty on your head, for a jaunt on your favorite trail. There are no bugs now, and even if there were, they would have a hard time getting to your skin through all those layers of clothes. The woods are without leaves, so you can see more of the lay of the land. Even though much of the life of the region is dormant, there are still some interesting things to find.

One of those bits of life is a double treat wrapped in one package. Lichens seem to be simple organisms, but, in fact, they are a complex combination of two, sometimes more, organisms. They are a combination of a fungus -- non-green, plant-like organisms we recognize more familiarly as a mushroom or toadstool -- and a green alga -- a single-celled plant usually found in ponds and lakes.

The amalgamation of these two organisms is to the mutual benefit of both. Biologists call this symbiosis -- two different organisms living together, with both benefiting.

The relationship was first discovered in 1869 by a German, Simon Schwendener. He wrote: "As a result of my researches, the lichens are not simple plants, or ordinary individuals in the ordinary sense of the word; they are, rather, colonies, (in) which, however, one alone plays master, while the rest, forever imprisoned, prepare the nutriments for themselves and their master."

Schwendener's view was that the lichen was the prison, and the algae the captive slaves supplying food. Lichenologists, biologists who study lichens, have long discussed this view, and there are many questions about the exact benefits passed between fungus and algae in lichens.

One point of agreement is that the relationship allows lichens to colonize many habitats that neither fungus nor algae would otherwise find suitable. Fungi usually need decaying organic material to live, but lichens can survive on bare stone and in the salt spray of seaside rocks.

Algae usually are in wet shaded habitats or water, but, in lichens, can live on the dry bark of trees on sunny mountain summits.

Generally, lichens are layered organisms, with the fungal portion being the most prominent part of the structure.

This fungus in lichens is very different from familiar mushrooms we find. Those have a mass of thin thread-like filaments below ground. The parts we see as mushrooms, toadstools and puff balls are actually the fruit, or reproductive part, of the hidden subterranean fungus.

Lichens, still part fungus, are above ground year-round, and the fruiting bodies are small. Some lichens have a thin leafy body just a few cells thick; others are cylindrical; some, tiny cups; others, a lump of tissue; and still more, simply a thin crust over rock or bark.

Between the layers of fungus cells are the algae cells, Schwendener's prisoners.

The tough outer fungus cells protect the delicate algae, which are usually just below the upper surface. There, algae can gather light necessary for them to photosynthesize. Remember, algae are green plants, primitive relatives of grass, wildflowers, and trees, and need light to live.

I'm often asked, "What good is it?" Most often, the question is asked from a human viewpoint; in other words, "How does it benefit people?"

In the case of lichens, they have been used as medicine by ancient civilizations from China to Egypt to Native Americans. Reindeer moss, actually lichen and not a true moss, is found in Christmas wreaths and is used in model railroading to resemble scale vegetation.

The most significant commercial use of lichens is as dyes. Species in the family Roccellaceae , found along rocky coasts, are mentioned in the Old Testament for their reddish-purple dye. In Sweden, a species with the common name of the candle lichen is used to color animal fat to make, of course, candles.

The most unlikely place we find lichens is in perfumes and cosmetics. In southern France, oak moss, again lichen and not a moss, is collected. Using solvents, an essential oil with a musk-like fragrance is extracted from and used in perfumes and other products with subtle delicate scents.

Getting back to the original question of "what good is it?," my answer is usually prefaced by a short lecture that the value of an organism, or other part of nature, is not necessarily associated with human value. There are many other roles that plants, animals, fungus, algae, bacteria, rocks and rivers have other than to be used by and benefit humans.

The ecological role of all natural things is as important as human uses.

On earth, lichens make up 8 percent of the vegetation. That seems like a lot of lichens to those of us familiar with Western Pennsylvania. However, in the arctic, tundra covers thousands of square miles, and the dominant vegetation is lichen mats. Like other vegetation, where lichens cover the ground they conserve moisture and hold the soil in place. Because lichens have imbedded algae that photosynthesizes, that process takes carbon dioxide and water and combines them with light energy to make food and release oxygen. Thus, lichens are a carbon trap slowing global heating.

Lichens are found on every continent including Antarctica. They can be found from the summits of alpine peaks to the edge of oceans, from spruce forests to the tropics.

In the extreme environment of bare rock, lichens are the first to begin making soil.

The thin flaky body of lichen is held to solid rock by the same filaments that are the main body of fungus in moist soil. These tiny threads push into the microscopic cracks and widen the crevice. Finally, little cracks become big cracks, and the rocks break. Lichens also produce acids that dissolve rock and add nutrients to new soils.

It takes a long time to crunch a massive mountain into a flat sand beach, but lichens are the first to get the process going. They pioneer in the erosion business, an enterprise that is constantly changing the face of the planet.

Many birds incorporate lichens into their nests, and animals from insects to reindeer eat them as food. Lichens are part of the diet of native wild turkeys.

Finally, in the past 30 years, a natural value of lichens has been as a biomonitor. This assessment process uses living organisms to judge the quality of air or water.

When growing lichens are exposed to air with very, very small amounts of sulphur dioxide, fluoride or other toxic gases, they die. A lack of ubiquitous lichens in an area indicates poor air quality. That same poor air could be dangerous for humans. Prior to clean-air legislation of the 1970s, lichen populations near cities were scarce. Now, with improved air, lichens are returning to urban and industrial areas.

Here in Western Pennsylvania, you can find lichens in all sorts of places.

As I hike the Great Allegheny Passage near Confluence, in Somerset and Fayette counties, the tree trunks are decorated with beautiful, symmetrical, flaky, light-gray lichen medallions.

So, get yourself bundled up for the winter and revisit one of the trails you walked last July. You probably didn't notice them then, but with all the other natural distractions dormant, you are likely to find the double organism, a fungus and algae combined in the lichen.