Description: This unmistakable crustose lichen has a characteristically bright, red-brown thallus — sometimes dulling in shaded situations — with flat, black discs with no surface ornamentation. It occurs mostly on hard, siliceous rocks and is especially abundant where the geology includes formations with a high iron or metal-bearing content. It is scattered in suitable habitats throughout Ireland.

Key Identification Features:

• The rich, reddish-brown colour helps to indicate this species. Rhizocarpon oederi is similar, but the discs have a spiral, or creased (gyrose) surface ornamentation (best seen with a lens)
• Usually associated with acid rocks that are rich in quartz and/or metal-bearing minerals.

Original text submitted by Simon Davey

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

iNaturalist: Tremolecia atrata at iNaturalist World Species Observations database.