Urban Ecology

Lots to Like About Lichen

by Diane Boudreau

Like a layer of paint, lichens add color to the landscape without calling attention to themselves. Hikers marvel at cacti and wildflowers. Rarely do their eyes linger on the rough blue-green crust that carpets rocks and tree trunks. However, these understated plants are important, hardy, and even beautiful when one stops to notice them.

They are the most important organisms in some ecosystems, such as the coastal areas of Baja California, says Thomas Nash, an ASU plant biologist. Lichens are very sensitive to air pollution. As a result, scientists rely on them as bioindicator species, a sort of natural early warning system.

Lichens produce unique secondary metabolites, some of which are important in the pharmaceutical industry as anticancer agents, adds Nash. They are also important in breaking down rocks and holding soil in place.

Lichens are actually made up of two plants, an alga and a fungus, living in a symbiotic relationship. In the desert, lichens dry out completely and remain dormant until rain or dewfall provides enough moisture to make them active again. This ability allows lichens to survive some of the harshest environments on the planet.

The Sonoran Desert and surrounding regions are home to more than 40 percent of the lichens known to North America. Until now, these species have never been catalogued in one place.

Volume I of the Lichen Flora of the Greater Sonoran Desert Region covers nearly 600 species of lichen in more than 140 genera. The volume is co-edited by Nash, Bruce D. Ryan, Corinna Gries, and Frank Bungartz. It is largely based on collections in the ASU lichen herbarium, which boasts more then 90,000 specimens.The book offers identification keys and descriptions for each species treated, as well as maps showing species distribution.

For the past 30 years, Nash has collected lichens extensively throughout the region, which includes all of Arizona, the desert regions of southeast California, and coastal Californian areas as far north as San Francisco. In Mexico it includes Baja California, Sonora, Sinaloa, and the Sierra Madre area of western Chihuahua.

The book will ultimately be part of a three-volume set. Nash says the second volume should be published by summer 2003.

For more information, visit http://nhc.asu.edu/lichens/flora/flora.jsp
Or e-mail Thomas Nash Ph.D., Department of Plant Biology.