Description: This chalky-white, non-sorediate, non-isidiate lichen of basic rocks can only be confused with Rhizocarpon umbilicatum (medulla = K+ yellow, Pd+ orange) when in this environment. On acid rock, similar coloured Porpidia crusts usually turn out to be P. cinereoatra (described elsewhere). P. speirea has an Iodine + violet medulla, confluentic acid and immersed discs. In Ireland, the species is thinly scattered.

Key Identification Features:

• Thallus chalk-white, discs immersed; medulla K-, Pd-
• Always on hard, basic rock.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Porpidia speirea at iNaturalist World Species Observations database.