Like all green plants I photosynthesize, that is I make my own food, here simple sugars, that I metabolize further to give me energy. All I need from the environment is light, water and some good rich soil to put down my roots.
Lichens esseniatlly can utilise sunlight, water and air to grow! This requires the combination of the properties of fungi (Nitrogen acquistion) and the photosynthetic partner, be it another fungi or a Cyanobacterium.
. The fungus gives some protection against UV radiation and desiccation, while the photosynthetic component can work at very low temperatures, even below -40 degrees. They can also have a compound present that also stops the Lichen ‘freezing’ -something like Anti-Freeze!