Rhizocarpon geographicum (L.) DC.

Rhizocarpon geographicum forms a perfect mosaic of yellow thalline areoles and black lecideine apothecia. The prothallus is black. It is never parasitic, not even in the early ontogenetic stages. It is a polymorphic species with many varieties and certainly requires a worldwide revision using molecular data.

The lichen is common and abundant in both hemispheres and probably is the most common Rhizocarpon species in Europe. In the Czech Republic, it grows from the lowest elevations to the highest mountains, where it is often noticeable from a distance, dominating siliceous rocks and screes. In the lowlands, it often grows on anthropogenic substrates, such as roof tiles, clearance cairns and walls. Generally, the species has a wide ecological amplitude. It is found on exposed to partly shaded rocks, strongly acidic to basic silicates.

Ascomycota → Lecanoromycetes → Rhizocarpales → Rhizocarpaceae → Rhizocarpon