Lichens

A lichen is created by the union of a fungus and an alga. As in the case of a successful marriage, these partners live together in harmony. Although some say that the fungus is parasitic on the alga, thereby distorting the alga, such an association is sufficiently successful to enable a single lichen to survive for several thousand years.

Lichens have scientific names, as do their components; thus, the fungus has a name, the alga has a name, and the association has a name

Lichens grow in harsh environments: on rocks and the trunks of trees: in salt spray, the desert, the arctic, and tropical forests. Yet lichens are sensitive, and their presence or absence can be used as an indicator of pollution. For example, lichens often do not grow well on the trunks of trees in the city.

Lichens may be crustose, foliose, or gelatinous. Some crustose lichens seem to be painted on the substrate. Verrucaria maura is a lichen that forms a distinct black band just above high tide along the New England coast.