They tend to live for many years, and lichens hundred of years old can be used to date the rock surfaces on which they grow. Lichens spread mostly by small pieces of their body being blown around. All the partners in the original lichen body are present in the fragment, so growth can begin immediately. Some lichens create soredia, balls of tissue made just for dispersal. Although the fungus is the major partner, dispersal by spores is rare.
Lichens have many uses.
They differ in their sensitivity to air pollution, and the presence or absence of different lichens in an area has been used to map concentrations of pollutants. Foliose lichens are used to represent trees in model train layouts. It is thought that these chemicals are produced by lichens as defenses against disease and parasites, and, in some cases, to make the lichen taste unpleasant to animals. Other secondary products are used to make everyday life more colorful and pleasant. Some are used to scent soaps and make perfumes.