Lichens:
The “Tough Guy” Plants

Lichens are among the weirdest-looking plants, and they live in strange places.

You may find them growing on tree branches or brick walls. In the Arctic, they grow on the ground as a mat. Reindeer paw through the snow to find lichens (LIKE-ins), which are their most important winter food.

Scientists have collected lichens from crevices in Antarctic boulders and from old skulls bleaching in the desert. Some lichens have been growing on old stone monuments for centuries.

Lichens are so hardy that they can survive even after they dry to a brittle crust in the sun. When rain falls, the lichens soak up water and begin growing again as if nothing had happened.

What makes lichens so different from other plants?

Each type of lichen is a partnership between two forms of life. The first is a one-celled green plant called an alga. The alga lives inside the second partner. That partner is a fungus, which is related to yeast and mushrooms.

The algal cells of a lichen capture the energy of sunlight and the carbon dioxide in the air to make food for both partners. The fungus is a tough, moisture-holding house for the alga.

The name for this special kind of partnership is symbiosis. The lichen symbiosis allows the two different organisms to do things that neither could do alone.

By themselves, one-celled green algae must live in water or as a thin film in damp places, such as a coating of green on a flowerpot. Fungi cannot make their own food. Most of them live on decaying things, like wood or leaf mold. But when they are together, the alga feeds the fungus and the fungus protects the alga.

In addition to being tough, lichens make acids that taste bitter to most animals. The fungus can produce these acids only when working together with its partner alga.

No one knows just how algae and fungi joined up to become lichens. Scientists can separate the algae from the fungi and grow them separately. But it’s much harder to put the partners back together again.

In nature, most lichens spread without separating into algae and fungi. Instead, small bits break off and are carried away by rain and wind. When a piece settles onto a good spot, a new lichen grows.