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Lichen. Coloured scanning electron micrograph (SEM) of the spores (green) of lichen (Cladonia sp.). The ball-shaped structures are are asexually produced spores 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 nutrients through photosynthesis by the algal cells, and also absorb minerals from rainwater or acidic digestion of the substrate. They can reproduce both sexually, as fungal only spores, or asexually, as balls of fungal hyphae containing algal cells. Cladonia are classified as fruticose lichen, which are lichen with free standing erect structures. Magnification: x1600 when printed 10cm wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE/SCIENCE PHOTO LIBRARY)