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Lichen. Coloured scanning electron micrograph (SEM) of the spores (green) of Cladonia lichen. The ball-shaped spores are asexually produced and known as soredia. Lichens are organisms formed by the symbiotic association of a fungus and a green alga or cyanobacterium. They are able to produce food energy through photosynthesis by the algal cells, and also absorb minerals from rainwater or acidic digestion of the surface. They can reproduce both sexually, as fungal only spores, or asexually, as balls of fungal and algal soredia. Cladonia are fruticose lichen, which are lichen with free standing erect structures. Magnification: x80 when printed 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE/SCIENCE PHOTO LIBRARY)