Lichens are a community formed by an alga and a fungus. Algae provide the ability to photosynthesize, while fungi provides structure and nutrients. Sometimes a cyanobacterium is involved, which provides the community with additional nutrients. Lichens grow in our forests, but also high up in the Alps, where it is too cold for many other organisms. They have few demands on their environment and can easily cope with little nutrients. An interesting mechanism of lichens is that they dry out under unfavourable conditions and can then reabsorb water from the environment.
Explanation for children:
Lichens are a community of an alga and a fungus. The alga and the fungus are friends and help each other: the alga makes photosynthesis and gives the fungus sugar, and the fungus grabs many nutrients with its fungal filaments and shares them with the alga. Sometimes a cyanobacterium is involved, which provides the community with additional nutrients. Lichens grow in our forests, but also high up in the Alps, where it is much too cold for most creatures. A special mechanism is that they can simply dry out. When there is enough water again, they absorb it like a sponge.