Description: Thallus crustose relatively thick and dark brown. Individual specimens circular with concentric growth rings but often confluent with overlapping lobes growing to several cms across. Fairly well attached with loose raised margins.

Habitat: Abundant. Epilithic or epizoic especially on limpets but not epiphytic.

Distribution: All around the shores of the British Isles. Europe: Mediterranean and the Black Sea, Portugal, Atlantic coasts of Spain and France, Belgium, Netherlands, Germany, Denmark, Baltic Sea, Sweden, Norway, Faroes and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Connecticut and Long Island, Delaware and Virginia. Further afield: Canary Islands, South and east Africa, Japan and New Zealand. Probably cosmopolitan in temperate and subtropical coasts.

Key Identification Features:

• Encrusting, thick and brown, showing concentric rings and raised margins.

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

iNaturalist: Ralfsia verrucosa at iNaturalist World Species Observations database.

WoRMS: Ralfsia verrucosa at World Register of Marine Species. Accepted name: Pseudoralfsia verrucosa (Areschoug) Parente, Fletcher & G.W.Saunders, 2020. AphiaID: 1771402.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Fucophycidae; Ralfsiales; Ralfsiaceae; Ralfsia