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

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