Lichen (Lobaria virens), close-up. A lichen is composed of a fungus and an alga growing in a mutualistic (mutually beneficial) association. The alga produces nutrients for the fungus and the fungus protects the alga from harsh conditions. Many brown cup-shaped apothecia (fruiting bodies) are visible on the lichen. These are spore- producing structures formed by the fungus. The spores produced in each apothecium can grow into new fungal components. Lobaria virens is very susceptible to air pollution, and is commonly found only in rural areas. However, it is resistant to extremes of heat and cold, and can survive in droughts. Photographed in Scotland.