A lichen is a symbiotic community – i.e. useful for different species – between fungi and a partner that converts light into chemical energy carriers by means of photosynthesis. Only in symbiosis do completely new structures and growth forms develop, which only exist in lichens.

In a 2008 experiment, biological samples of the ‚ornamental yellow lichen‘ (Xanthoria elegans) were exposed to hostile conditions in space for a year on the Interna- tional Space Station ISS. Thanks to their high adaptability, the samples were able to withstand the adverse conditions. The high resistance of lichens is also evident in climatic changes: In heat and drought, for example, they become inactive. Only when they take up water again, via rain, dew or humidity, is their metabolism reactivated. This is how lichens can live up to 5000 years.