Description: This small, mosaic-forming epiphyte consists of straight, flattened discs sprinkled about the bark in patches. The yellowy, orange-flushed thallus is immersed in the bark surrounded by an orange-brown margin. The pointed or star-shaped, purple-brown discs (0.3-1.6mm long) are sometimes powdered red along the edges. It grows mostly on smooth bark, for example, hazel and young oak. North and west Ireland. The discs turn purple with a dab of K (Potassium hydroxide).

Key Identification Features:

• The straight or jagged, star-shaped discs, K + purple with red powdery edges (pruina) and habitat of smooth bark in old woodlands should distinguish it
• Arthonia cinnabarina is similar but has larger, more rounded discs: pink powdery or brown.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Coniocarpon fallax at iNaturalist World Species Observations database.