Jelly lichen. Coloured scanning electron micrograph (SEM) of a section through jelly lichen (Collema fuscovirens). Lichens are organisms formed by the symbiotic association of a fungus and an alga (green spheres) 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. Collema lichen are classified as foliose due to their flat appearance and leaf-like structures. They are found on rock surfaces and appear as dark and gelatinous when wet. Magnification: x680 when printed 10 centimetres wide.