How do lichens grow?

Lichen is a fungus associated with algae. It grows where no plant can live: on the top of a mountain, on rocks by the sea, on chilled lava, etc. When rotting, fragments of lichen form a soil rich enough for moss and other plants. They are flat or bearded, yellow, orange and black. More than 20,000 species of lichens have been discovered.
In a lichen, the fungus protects the algae. He gives her water and mineral salts. The seaweed produces sugar and other foods, which it shares with the mushrooms. It’s a symbiosis a bit like coral. But due to pollution, some lichens die: by observing them, you can find out if the air is clean.