Living as a single organism, a lichen is a colony of two or more different organisms... green algae and/or cyanobacteria, and fungi.

Within a lichen, the algae or cyanobacteria produce food by photosynthesizing; the fungi retain moisture and give support and structure to the lichen.

A phrase to help remember some of the specifics of a lichen is "Alice Algae took a liken to Freddie Fungus."

For many years, lichens have been considered a classic example of mutualistic symbiosis. Symbiosis is a relationship that exists between any two organisms. In mutualism, both organisms benefit.

Recently, scientists have found evidence to suggest that symbiosis in a lichen may be commensalism or parasitism. Commensalism occurs where one organism benefits without affecting the other. Parasitism occurs when one organism benefits at the expense of the other. The species of algae and cyanobacteria in a lichen are capable of living independently, while fungal species found in lichens cannot. That is a commensalistic relationship. Some photosynthetic organisms are destroyed during the exchange of nutrients within a lichen. That is a parasitic relationship.

Lichens grow on a variety of substrates including rocks and trees. Each lichen species has its own form. Forms are classified as being 1) crustose ... paint-like, 2) foliose ... leafy, 3) fruticose ... branched, or 4) gelatinous ... thick and gluey

Lichens have important functions in the environment. They remove pollutants from the air, provide food for some animals, provide nesting material for birds and small mammals, and may protect trees from losing moisture during drought.

Historically, people have used lichens in many ways. Various species have been used for dyes, litmus paper, perfumes, cosmetics, fiber, poison for arrowheads, embalming, food, and medicines (antibiotics for boils, scarlet fever, and pneumonia; fungal remedy; and treatment for ulcers and burns.) Today, lichens are used as reliable environmental indicators. They cannot survive if air is badly polluted with sulphur dioxide. If air is clean, they are plentiful.

Along the hammock trail at the Conservancy of Southwest Florida Nature Center, you will see several different species of lichens.