Description: This widespread lichen of siliceous rock outcrops and sea cliffs is easily identified. The thallus, a dirty grey with a hint of brown, can be smooth, broken up into little islands (areolate) or warted. The distinctive feature of the species is the short, rounded, brown-tipped isidia (minute structures containing fungal hyphae and algae). These are easily overlooked at first owing to their small size. Magnified many times they would resemble beads spilled over the surface of a pavement. The isidia, thinly attached at their base, are easily removed by pressure so that in some specimens all that is visible through a lens are scar-like craters. Discs are rare, semi-globose hidden in warts. A dab of potassium hydroxide (K) will turn the thallus yellow changing to blood-red within a minute.

Key Identification Features:

• Greyish thallus, minutely crowded with brown-tipped, bead-like isidia
• A dab of K turns the thallus yellow, changing to blood-red; on well-lit siliceous rocks.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Pertusaria pseudocorallina at iNaturalist World Species Observations database.