FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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WHAT AM I? -- A LICHEN
By Kathy Korbholz Lichen comes from the Greek word leichen meaning tree moss. Although lichens appear to be independent organisms, they are not. Each lichen species is a synergistic partnership of a particular fungus and a particular alga. Nearly 1000 species of lichens are found in California. The algal cells utilize sunlight to produce food, while the fungus provides structure and probably protection for the alga. The fungus determines the major structure of the lichen which is called the thallus. Some scholars debate whether the relationship is truly symbiotic, mutualistic or parasitic. Lichens have very simple physiological demands. Mineral nutrients come from dust, dew, fog, and rainwater and are eagerly taken up by the thallus. When dry, lichens enter a dormant phase and can endure long periods of drought and extreme temperatures. When moistened, they are ready to resume growth at once. The result is that lichens have invaded and thrive in almost all habitats from desert to polar. Often mosses are their only competitors. Because they remain dormant much of the time and grow so slowly (usually 1-10 millimeters per year) they are considered Methuselahs among living organisms. Some arctic species are estimated to be 5000 to 9000 years old—nearly twice the age of bristlecone pines in California. For weavers and fabric manufacturers, brilliant lichen colors make unusual textile dyes. Native Americans used lichens to color porcupine quills to weave into their baskets, Europeans used lichens to dye wool, and a rare coastal lichen from southern California is used to make litmus paper. Lichens are used to this day in European perfume making. Their antibiotic properties are still used in China and were probably as popular with native Californian Indians as they are today with Seminoles in Florida. With no excretory system to rid their thalli of contaminants, lichens are very sensitive to pollution. The very presence or absence or lichens is a useful biological indicator of contamination. They have been collected in and around cities to measure the concentrations of lead and other toxic materials in the thalli. Lichens are divided into three common growth forms. The simplest, Crustose, grows firmly attached to rocks, bark, or other surfaces and appears as a crust on objects. Some are so fine and tightly attached, they almost look like a coat of old paint. The second, Foliose, looks like leaves or foliage. It can be tightly or loosely attached to the surface, often with root-like threads called rhizines. Its wrinkly surface is more or less flat. The third, most complex type, is called Fruticose. These lichens are attached to the substrate at only one point. They may grow erect and resemble scrubby little bushes or may hang down from branches as gray green streamers. They are often misidentified as Spanish moss.
This year’s greater-than-normal rainfall presents the perfect opportunity to appreciate these fascinating organisms. In Edgewood, just look for the velvety green attached to branches of trees and shrubs; even broken branches and twigs on the ground offer specimens. Then study larger rocks next to the trail to view the bright yellow and orange lichens. Try the Clarkia Trail. The upper portion offers eye-level foliose and fruticose lichens on the serpentine chaparral. Along the lower portion of the trail, you can find a magnificent collection of crustose lichens on a huge serpentine outcropping right next to the trail. |
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Most
authorities believe lichens are not parasitic and do not harm the trees on which they grow
except possibly by shading leaves below them. In fact, they benefit the landscape by
pioneering on bare rock, eventually breaking it down into soil fit for leafy green plants.
Soft-textured fruticose and foliose lichens enhance the beauty of the forest, while
brightly colored crustose lichens can transform a barren rocky landscape.