Trumpet lichen. Coloured scanning electron micrograph (SEM) of a section through trumpet lichen (Cladonia fimbriata). Lichens are organisms formed by the symbiotic association of a fungus and a green alga or cyanobacterium. The algal cells use photosynthesis to produce nutrients which are absorbed by fungal hyphae that surround and penetrate the algae. Fungal hyphae also absorb minerals from rainwater or acidic digestion of the substrate. Cladonia lichen are classified as fruticose lichen due to the presence of erect structures. Magnification: x21 when printed 10 centimetres wide.