Description: An encrusting calcified alga up to 10 cms in diameter, very thick, up to several mm. Young plants have a thick margin. Smooth becoming knobbly or crested with overlapping lobes. Margin without orbital ridges.

Habitat: Very common. Epilithic in the midlittoral to 8 m depth.

Distribution: British Isles including the Shetlands. Europe: Mediterranea, Portugal, Atlantic coastSpain, Norway and the Faroes. Further afield: Canary Islands.

Similar Species: Phymatolithon purpureum is similar but has orbital ridges.

Key Identification Features:

• Thick - to several mm and chalky in texture. Without orbital ridges and with a smooth surface. Overgrowing most other encrusting algae.

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

iNaturalist: Lithophyllum incrustans at iNaturalist World Species Observations database.

WoRMS: Lithophyllum incrustans at World Register of Marine Species.