Description: This crustose epiphyte occurs mostly without discs (that is, in the sterile state), so is easily confused with other species which have a yellowish thallus and a C+ orange, spot test reaction. Since it grows equally well on the rough or smooth bark of well-illuminated deciduous trees in undisturbed woodland, parkland or along waysides, the key to its identification lies in the thallus which is yellow-green with abundant rounded isidia which soon dissolve into soredia. In fact they can often obscure the thallus completely. It has a more intense, green-yellow appearance than any of its look-a-likes and is UV+ orange (a standard UV source will confirm this). In the herbarium of museums it can retain its fresh colour for years. Lecanora expallens is thinner, duller and UV-; Pyrrhospora quernea has a brown tinge and is very finely granular; Ochrolechia inversa is UV+ pink, has fine-powdery soralia, is paler, almost beige in colour. Thinly scattered; absent from south-east Ireland.

Key Identification Features:

• Almost luminous yellow-green thallus with rounded isidia which dissolve into soredia
• UV+ orange.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Pertusaria flavida at iNaturalist World Species Observations database.