A guide to lichens on twigs

What are lichens?

Lichens are composite organisms made up of a fungus and one or more algae living together. The algal partner produces essential nutrients for the lichen through photosynthesis, while the fungal partner provides the body in which they both live. The fungus produces spores in fruiting bodies (apothecia), which must germinate and find an algal partner before they can form a new lichen. In order to avoid this difficult stage many lichens produce minute fragments containing both partners, which can quickly colonise available habitats. These fragments can appear either as finger-like outgrowths (isidia) or sugar-like granules (soredia).

Xanthoria parietina

Lichen names

Very few lichens have common names, but each lichen species has its own Latin name, e.g. Xanthoria parietina (L.) Th. Fr.

Like your name, Latin names have two parts. The first part is the name of the genus in which closely related lichens belong, like your surname (eg Xanthoria). The second part is the species name, like your first name, which belongs to organisms sharing the same features (eg parietina). After the lichen name is the abbreviated names of the person(s) who named the species (in this case L. for Linnaeus and Th. Fr. for Theodor Fries).