Lichens can absorb large quantities of water. Their fresh weight is often a multiple of their dry weight. On the other hand are they rather unaffected by desiccation. They are able to survive longer periods of dryness without damage. The lichen thallus is species-specific.
Lichens belong usually to the most unpretentious organisms.
Lichens thrive also on rocky subsoils, an ability that is hardly shared by plants and fungi. Fungi lack the organic substrate in such an environment, multi-celled plants cannot cope with the short periods of vegetation characteristic for extreme biotopes, and algae are too sensitive to desiccation. These difficulties resemble the situations that must have predominated the earth s surface before it was largely covered by vascular plants and their precursors. The versatile nature of lichens is also displayed by the fact that they were able to survive in large parts of the earth even when they became inhabited by plants. Lichens adapted easily to the new conditions.