Have you ever gone for a walk in the woods? If you have, you may have seen colorful things growing on tree trunks and rocks. They look like plants, but they aren’t. They are called lichens. Lichens are made of two living things: a fungus and an alga. They live together and help each other.
How do these living things help each other? The alga makes food from air and water. The fungus protects the alga by growing around it.
Lichens have no roots. They don’t need soil to grow. They can grow in strange places—on rocks, cliffs, and tree trunks. In the Arctic and Antarctica, lichens grow on rocks.
Lichens grow slowly. They can grow in cold temperatures. They can even keep growing when covered in snow!
Lichens are tough. If a lichen gets dry and cold, it might crumble and blow away in the wind. But it isn’t dead. When it is warmer or wetter, the lichen might start growing again.
Lichens are important. Caribou eat them in the winter. People use them to make dyes and medicines. Scientists study how they can warn us about pollution.

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