Recommended Web sites:

Oregon State University's Lichenland Web site provides the basics about lichen biology and explains how to identify these mysterious organisms. Visit ocid.nacse.org/lichenland/.

You can find plenty more information about—and pictures of—lichens at www.backyardnature.net/lichens.htm (Backyard Nature), www.ucmp.berkeley.edu/fungi/lichens/lichens.html (University of California Museum of Paleontology), www.lichen.com/, and en.wikipedia.org/wiki/Lichen (Wikipedia).

For information about evolution, go to evolution.berkeley.edu/ (University of California, Berkeley), and www.pbs.org/wgbh/evolution/ (PBS).

Sohn, Emily. 2006. Assembling the tree of life. Science News for Kids (May 31). Available at http://www.sciencenewsforkids.org/articles/20060531/Feature1.asp .

______. 2005. Fungus hunt. Science News for Kids (July 13). Available at http://www.sciencenewsforkids.org/articles/20050713/Feature1.asp .

From The American Heritage® Student Science Dictionary, The American Heritage® Children's Science Dictionary, and other sources.

alga (Plural algae) Any of various green, red, or brown organisms that grow mostly in water, ranging in size from single cells to large, spreading seaweeds. Once classified as plants, they are no more. Like plants, algae manufacture their own food through photosynthesis. Unlike plants, they have no roots, stems, or leaves. They form a major component of marine plankton and are often visible as pond scum. Most are now viewed as being protists—a kingdom separate from plants and animals.

DNA Short for deoxyribonucleic acid. The nucleic acid that is the genetic material determining the makeup of all living cells and many viruses.

evolve 1. To undergo evolution. Birds may have evolved from reptiles. 2. To develop a characteristic through the process of evolution. Cats have evolved an extraordinary sense of balance. 3. To undergo change or development: Butterflies evolve from larvae.

fungus (Plural fungi) Any of a wide variety of organisms that reproduce by spores, including the mushrooms, molds, yeasts, and mildews. The spores of most fungi grow a network of slender tubes called hyphae that spread into and feed off of living organisms or dead organic matter. The hyphae also produce reproductive structures, such as mushrooms and other growths. Fungi are grouped as a separate kingdom from plants in taxonomy.

lichen An organism that consists of a fungus and an alga living together in a symbiotic relationship. The alga supplies nutrients by photosynthesis, while the fungus shades the alga from excessive sunlight and supplies water by absorbing vapor from the air. Lichens often live on rocks and tree bark and can thrive in extreme environments.

photosynthesis The process by which green plants, algae, and certain bacteria make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using light as energy. Photosynthesis normally releases oxygen as a by-product.