Lichens(地衣) cover as much as 8% of the planet's surface, an area larger than that covered by tropical rain-forests. They can be found growing on bark, rocks or walls; in woodlands, deserts or tundra.
Some lichens are familiar to the herbalists who find uses through the "Doctrine of Signatures"(形象学说). For example, species of Lobaria are used to treat lung diseases because of their lung-like appearance. Lichens have also been used for their chemical components. Lichens provide natural dye(染色) stuff in many traditional cultures around the world, including the famous Harris tweed woolens of Scotland. Lichens are also used in the production of perfumes. For example, "oak moss" was used as a component of several high quality French perfumes in the late nineteenth and early twentieth centuries.
Lichens also provide many important ecosystem services. Lichens contribute to biodiversity—they are found in all biomes. Some lichens are pioneers, so they are often the first to occupy newly exposed surfaces. Lichens also contribute to nutrient cycling. In some old-growth forests, lichens contribute up to 50% of the nitrogen. Many animals use lichens. Up to 90% of reindeer's winter food consists of lichens, and other animals use lichens for nesting material or hiding places. Lichens can also inform us about the condition of our environment. Many lichens require very specific environmental conditions. For example, presence of certain lichens can be an indicator of climate change. Some lichens are sensitive to air pollution and will disappear when air quality is poor.
Lichens are important also because they are beautiful to look at. How colorful would the rocks and cliffs be in the Rocky Mountains without the reds, yellows and greens of the crust lichens? Without these living creatures, our natural areas would look pretty boring and a little more lifeless.
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