Lichens of the Miller Springs Nature Center
A nature guide to the non-crustose lichens found on trees
Jerry D Evans
Have you ever wondered what that gray stuff is that grows on tree trunks? Just look at it after a rain and it appears to "light up". But what is this unusual form of life? It is an organism called a lichen. It is actually two plant-like organisms all rolled up into one. On the outside a lichen usually appears to be gray. But if it is sliced with a razor blade, just beneath the surface is a narrow layer of green due to the presence of algal cells. Algae are plant-like organisms that grow most abundantly in water. They make lakes and ponds green. Because algae contain chlorophyll, they make their own food by photosynthesis. The rest of the lichen is a fungus (mushroom group). The fungus protects the algae, while the algae makes food for both of them. This mutual benefit is called a symbiotic associatiion. Lichen are good biological indicators of air pollution and will die when exposed to air pollutants such as sulfur dioxide. Lichens can live in hot, dry places as well as in arctic conditiions. They live on rocks, on the ground, and on trees. About 15,000 kinds of lichens have been described. They come in many colors and shapes. Sizes range from one mm to more than three meters. Left undisturbed, lichens may live for centuries. One arctic species was found to be about nine thousand years old. They are easily collected at any time of the year, and identification of different species is not diffucult. With the help of a science teacher many projects with lichens are possible. Have fun with lichens.