OBJECT OF THE MONTH - September, 2004
Lichens
A crustose lichen growing on quartz rock.
The word lichen comes from the Greek, leichen, meaning a tree moss. Not really mosses, lichens are combinations of two different organisms, a fungus and an alga, growing together in a symbiotic relationship. Lichens come in a wide array of striking colors and various growth forms, called foliose (leaf-like), fruticose (shrub-like) or crustose (forming a thin crust on rock or other substrates).
The most striking aspect of lichens is their ubiquity. They occur worldwide and in most habitats. More than 15,000 species can be found from the canopy of tropical rainforests to the windswept rocks of Antarctica. Approximately 8% of the earth's surface has lichens as its dominant life form. It is likely that lichens play an important role in regulating the gaseous composition of the earth's atmosphere.
Lichens are sensitive indicators of air pollution. They contribute significant levels of nitrogen to old-growth forest ecosystems in the Pacific Northwest. Lichen crusts are important stabilizers of soil in desert areas. Some lichens have been used to date surfaces on which they grow by a technique called lichenometry. Species of Cladina in arctic regions are important food for huge herds of caribou.
The University of Colorado Museum Herbarium houses nearly 100,000 specimens of lichens—the 8th largest collection in the United States.