Rosette lichen (Physcia adscendens), coloured scanning electron micrograph (SEM). Lichens are organisms formed by the symbiotic association of a fungus and an 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. Physcia lichen are classified as foliose due to their flat appearance and lobed branches. This species has distinctive hair-like appendages at the end of branches (centre). Magnification: x34 when printed 10 centimetres wide.