Structure and taxonomy

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.

Glossary

apothecia- spore-producing fruiting bodies of the fungal partner.

foliose lichens - leaf-like lichens with spreading to upright flattened lobes that are attached to the twig from the lower surface of each lobe.

rhizines - root-like attachments from the lower surface of a foliose lichen. They may be simple (left), branched (centre) or bottle brush like (right).

soredia - paler (than thallus) powdery to granular propagules containing algal and fungal partners. Often occurring in specialised bodies called soralia (far left), on the lobe margins or ends (center left), on the upper surface in cracks (center right), or as dots (far right).

spores - produced in fruiting bodies following sexual reproduction.

thallus - the lichen body