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Crusty navel lichen (Umbilicaria crustulosa) on an acid rock-face in the Pyrenees Andorra by BOB GIBBONSSCIENCE PHOTO LIBRARY
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Lichens on a rock
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Map lichen (Rhizocarpon geographica) growing on a granite gravestone This type of lichen is known as saxicolous lichen as it grows on or among rocks
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