Looking at Lichens

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Published on: Oct. 2, 1998

Last revision: Nov. 2, 2010

Almost everyone is familiar with the term lichen (pronounced "like-in"), but few people know much about these small plantlike organisms. Lichens grow throughout Missouri and are a major contributor to the mosaic of colors in our natural landscape. They grow on all types of rocks and trees in a variety of habitats, and they are an important component of healthy habitats.

Lichens often are lumped with mosses or other small plants, although they have little in common except size and habitat because lichens have no roots, stems or leaves. Unlike most animals and leafy plants, a lichen is a fusion of two unrelated organisms. Every lichen is a combination of a fungus and algae or algaelike bacteria. Bread mold, morel mushrooms or the toadstools that sometime grow in our lawns are some familiar fungi. Algae are most familiar to us as the green scum on ponds and other slow-flowing waters.

The fungi and algae in lichens are usually different types from their free living relatives. While almost every lichen species has a unique fungus component, we often see the same species of algae in more than one type of lichen.

A lichen looks and behaves differently than either of its components do independently. The algae and fungi in a lichen combine to form something that is capable of reproducing itself, has a distinct appearance and range of habitats and in every other respect acts like a distinct plant. Certain lichens are found only in specific habitats, and some only grow on one kind of tree or rock. On the other hand, a single boulder or tree trunk in a natural habitat may support 30 or more different kinds of lichens. Much of the color we see on bluffs and rock outcrops is due to lichens.

The relationship between the algae and the fungi in a lichen is complex and not completely understood. This relationship also differs among different lichens. In general, lichens take their shape from the fungus component, within which are zones containing algae. Many lichens have brown or black disks on their surface-these are the spore-producing parts of the fungus.

The lichen fungi get nutrition from the algae, which use sunlight and simple chemicals to produce food. How much this relationship is mutually beneficial and how much is parasitic is uncertain. It is interesting, however, that lichens flourish in places where both algae and fungi are rare.

Most lichens grow slowly and many grow only in a narrow range of habitat conditions. This makes them especially susceptible to habitat disruption. Many species are sensitive to air pollution, and lichens are used throughout the world to assess and monitor air quality. Despite these sensitivities, lichens are capable of growing in the harshest of natural environments. They live in fresh and salt water, deserts, tropical forests, alpine summits and even in Antarctica.

Because of the slow, uniform growth rates of lichens, scientists use some species of them in polar regions to establish the time and speed of glacial retreat. Some tropical lichens even grow on the shells of beetles and tortoises. In Missouri we have nearly 500 different species of lichens, including some found nowhere else in the world. Lichens are found in every square mile of the state, although in urban areas they are fewer, smaller and easily overlooked.

Lichens often contain bitter chemicals and are not a major wildlife food source, but they are an important component of the food chain. Land snails and many other small animals feed on lichens. In northern tundra, lichens are a staple winter food of caribou and reindeer. Locally, deer sometimes consume small quantities of lichens, especially in winter.

Several birds, including the ruby-throated hummingbird, eastern wood pewee, and blue-gray gnatcatcher, use lichens in nest construction. One of Missouri's most colorful warblers, the northern parula, prefers either old man's beard lichen (Usnea) or Spanish moss for its nest. Spanish moss is a flowering plant related to the pineapple and does not grow as far north as Missouri. Local populations of northern parula warblers often use the abundance of old man's beard lichens in healthy Ozark woodlands.

People have used lichens since antiquity as medicines, dyes, food, decoration, perfumes and even crude clothing. The subtle browns of Harris tweed fabric come from dyes made of lichens. Artisans in Europe have used lichens for centuries to produce a vivid purple dye. The acid sensitive litmus paper that many of us remember from high school chemistry classes also is made from lichen extracts. Some antibiotic salves also contain lichen extracts.

Although not poisonous, lichens generally are not palatable to humans, and some people have developed rashes from prolonged contact with certain lichens. People use a few species for food, especially during hard times, and the "manna from heaven" described in the Bible is thought by some people to be a desert lichen. In Asia, a large, saucer shaped lichen called a rock tripe is often fried and eaten.

Many lichens are common throughout Missouri, and a few are so distinctive or colorful that they are noticed by those who regularly go outdoors. Even though they often cover tree trunks, lichens are not tree parasites and do not damage trees. Lichens play a critical role in mineral nutrient cycling in many forests. Certain lichens are even capable of using, or "fixing," atmospheric nitrogen-an unusual trait shared only by a few plants, such as legumes.

We are just beginning to understand the diversity and importance of lichens in our natural systems. The Conservation Department, in conjunction with researchers from The Nature Conservancy and the Missouri Botanical Garden, is studying the lichens of Ozark woodlands as part of its Missouri Ozark Forest Ecosystem Project (MOFEP). This and other ongoing work on Missouri lichens has resulted in the discovery of several species new to science, including two that have been named after the state of Missouri.

You can identify three general types of lichens by their shape and appearance. Lichens with a well-developed, three-dimensional growth form, often looking like miniature trees or columns, are called fruticose lichens. The best known local examples of fruticose lichens are British soldiers, old man's beard and reindeer lichen. Fruticose lichens are often the first to disappear when a natural habitat is disrupted.

Probably the most common type of lichen in Missouri is the foliose lichen. These are flat, typically green or gray lichens that can be abundant on trees and rocks, especially in the Ozarks. These lichens come in a wide range of sizes, with some species less than 1/4-inch wide and others that are more than 10 inches wide.

Crustose lichens are the most diverse and least noticed group of lichens in Missouri. Just as their name implies, crustose lichens often look like a thin crust on rocks, soil, trees, fenceposts, shingles and old, rusted iron on bridges. Some crustose lichens even grow inside rocks, occupying the microscopic spaces between rock crystals.

Most crustose lichens are small and drab and require a microscope for identification. Few have common names, although the bright orange fencepost lichen (Caloplaca microphyllina) is an exception that provides a splash of winter color on weathered eastern red cedar and Osage orange posts in prairie and farm areas. A few types of crustose lichens are among our most adaptable species and even thrive on concrete in downtown St. Louis and Kansas City.

Important yet tiny, colorful but often overlooked, lichens play an unusual role in our environment and in human consciousness. We seldom notice them, yet our landscape would seem less rich and varied without them, and many plants and animals indirectly depend upon them in our natural systems.

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