Description: This grey, crustose epiphyte with a distinctively zoned thallus margin is fairly straightforward in its identification. As discs are very rare, the beginner will notice first that the centre of the thallus contains slightly darker areas that are aggregations of small, brown-tipped, globose outgrowths (isidia), the shape of matchstick heads. A dab of Potassium hydroxide (K) turns the thallus yellow, then red. It is also Pd + orange. It occurs on the old, well-illuminated, nutrient-enriched bark of wayside trees, especially those forming avenues along drives or fringing the boundaries of woodlands. Throughout Ireland.

Key Identification Features:

• Grey thallus (on average: 3-6cm diam.) ringed by a zoned margin containing clusters of spherical, brown-tipped isidia, some of which may be branched
• Thallus K + yellow-red, Pd + orange; mainly on very well-lit wayside, field or parkland trees.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Pertusaria coccodes at iNaturalist World Species Observations database.