Description: This medium to dark brown crustose lichen occasionally suffused with hue of pink is a montane species, yet capable of surviving at lower levels around the edges of loughs and siliceous scree. Aesthetically, it is a rather beautiful species in its own right, outshining its lookalikes, R. jemtlandicum and R. hochstetteri, in the fashion stakes. It is a pleasure to section the thallus and explore the interior of the dusky black discs (to 1mm diam.) that arise from between the areoles. Within the discs are the one-septate dark brown spores. The addition of K (10% solution of potassium hydroxide) activates the pigments in the epithecium, which turn a glorious purple-red. In Ireland, the lichen is very rare: County Kerry.

Key Identification Features:

• Thallus brown, K+ yellow, Pd+ orange; discs with one-septate dark brown spores 26–36µm long
• Medulla I-; epithecium K+ purple-red.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Rhizocarpon badioatrum at iNaturalist World Species Observations database.