Description: Thallus encrusting and firmly attached to substrate. Confluent specimens to 10 cms in diameter.

Habitat: Common in the sublittoral. Epilithic in the sublittoral to 20 m or more.

Distribution: Widespread in the British Isles. Europe: Spain, France, Netherlands, Denmark, Baltic, Sweden, Norway, Faroes, Spitzbergen and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire and Massachusetts. Further afield: Alaska.

Similar Species: All other small brown encrusting algae are similar and require microscopic examination for determination.

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

iNaturalist: Pseudolithoderma extensum at iNaturalist World Species Observations database.

WoRMS: Pseudolithoderma extensum at World Register of Marine Species. Accepted name: Pseudolithoderma extensum (P.Crouan & H.Crouan) S.Lund, 1959. AphiaID: 144990.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Dictyotophycidae; Sphacelariales; Lithodermataceae; Pseudolithoderma