Lichens on a tree. Two types of lichen growing on a tree trunk. Lichens are mutualistic (beneficial) associations between a fungus and an alga, the al

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Lichens on a tree. Two types of lichen growing on a tree trunk. Lichens are mutualistic (beneficial) associations between a fungus and an alga, the alga occupying a single layer of cells within the body of the fungus. They are found growing on the surfaces of trees and rocks. On trees they are epiphytes: they live on, but do not harm, their host. Seen here is Parmelia sulcata (upper frame, blueish-green), common throughout the northern temperate zone. Also pictured is Rinodina roboris (centre, blue).

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Photo credit: © VAUGHAN FLEMING/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: algae, association, botanical, botany, epiphytes, epiphytic, fungi, fungus, lichen, lichens, mutualism, mutualistic, nature, parmelia, plant, rinodina, roboris, sulcata, support, symbioses, symbiosis, symbiotic, tree, trunk