Structure
A lichen is formed of two or more organisms, a fungus which forms the body of the lichen which in Xanthoria parietina consists of flattened spreading leaf-like lobes, and a green chlorococcoid alga which provides the nutrients for the fungus through photosynthesis.

Taxonomy
Xanthoria parietina belongs in the family Teloschistaceae which consist mainly of brightly coloured lichens that contain a compound that acts as both a sunscreen for the algal partner and also protects them from harmful UV rays. Hence Xanthoria is often found in sunny exposed places.