Description: This crustose lichen is very similar in appearance to R. petraeum (described elsewhere) which is also grey-white coloured. It lacks the concentric rings formed by the discs of that species and has a much thicker, chalky grey not pale grey-white thallus. The discs of R. umbilicatum are randomly scattered. R. umbilicatum grows on pure limestones, R. concentricum on rocks of a more intermediate nature. Throughout Ireland.

Key Identification Features:

• The discs are randomly scattered about the thallus, that is, they do not grow in concentric rings
• The thallus colour is chalky white or chalk-grey and grows on pure limestones.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Rhizocarpon umbilicatum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Rhizocarpon umbilicatum at iNaturalist World Species Observations database.