By Heather Paul Lichens are a partnership between at least two organisms - usually a fungus and an alga which grow together. This is called symbiosis. The fungus provides a protective home for the alga - protecting the alga from drying winds, strong sunlight and excessive wetting. The algae photosynthesise in sunlight and make food for both of them. Lichens are seen as “indicators”. Some species need clean air, whilst others thrive where there is pollution. The photo shows a grey-green beard...