• Visitors bask in a golden sunset at Dickey Ridge Visitor Center in Shenandoah National Park

    Shenandoah

    National Park Virginia

Lichens

Crustose Lichen

Sulphur-firedot lichen (Caloplaca flavovirescens), a crustose lichen

NPS Photo

If you visit a rock outcrop in Shenandoah National Park you are sure to find lichens. Lichens are a specific group of fungi unique because of their symbiotic relationship with green algae. In this relationship, the algae provide carbohydrates from photosynthesis to the fungus, while the fungus provides nutrients from decomposition to the algae.

Lichens are the first colonist on exposed rock. They secrete acids that gradually break down the rock surface on which they grow, contributing to soil development. Lichens grow extremely slowly, adding only 0.1 mm to 10 mm of growth per year. Much of the mineral nutrition needed by lichens is obtained from the surrounding air and precipitation to which they are exposed. For this reason, lichens are extremely sensitive to poor air quality, especially sulfur dioxide pollution.

 
Foliose Lichen

Smooth lungwort (Lobaria quercizans), a foliose lichen

NPS Photo

Lichens come in a wide variety of shapes and colors. They can grow flat against a smooth surface (crustose), extend from a surface like leaves (foliose), or form branched projections (fruticose). Common colors include black, white, orange, yellow, red, brown, and green. Sixty-nine species of lichen are known from Shenandoah National Park. Two of these species, map lichen (Rhizocarpon geographicum), and black crust (Melinelia stigia) are extremely rare in Virginia and found only on rock outcrops in the central district of the park. Other notable lichens within the park include the green foliose boulder lichen (Parmelia spp.) commonly seen on trees and rocks. And the large brown oval leaf-like projections of rock tripe (Umbilicaria spp.) often seen on large forest boulders.

Related Information

Useful references on lichens:

USGS Online Lichen Database: (Fact Sheet)
Lichen Collection the Smithsonian

Brodo, I.M. S.D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, Connecticut.

Websites that provide photographs and helpful biological information about lichens include the following:

Lichens of North America

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Did You Know?

Herbert and Lou Henry Hoover sitting on the porch of the Brown House at Rapidan Camp in Shenandoah National Park.

In 1928, wanting to escape the heat and humidity of summers in Washington, D.C., Herbert and Lou Henry Hoover began looking for a "summer place" within a day's drive of the city. The Hoovers acquired land within the proposed Shenandoah National Park and built Rapidan Camp, their summer White House.