Description: Encrusting thallus expanding to 20 cm in diameter. Closely attached to rock, to 4 mm thick, developing cylindrical knobbly to undivided branches. Margin without orbital ridges and with a smooth surface. Unattached branches grow and branch profusely and contribute to maerl beds.

Habitat: Low littoral rock pools into the sublittoral to 34 m.

Distribution: A northern species in the British Isles: England, Wales, Ireland, Scotland and Isle of Man. Europe: Spain, Portugal, Faroes, Iceland. Greenland. Atlantic coast of North America: Canada and Maine to Massachusetts. Further afield: Arctic Sea.

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

iNaturalist: Boreolithothamnion glaciale at iNaturalist World Species Observations database.

WoRMS: Boreolithothamnion glaciale at World Register of Marine Species.