Description: Thallus uniseriate growing in dense tufts to 25 cms long. Rhizoidal filaments form a thick cortex.

Habitat: Epilithic in the lower littoral and sublittoral to 6 m.

Distribution: South-west coasts of the British Isles including the Channel Islands. Europe: Portugal, Spain and France.

Similar Species: All species of Callithamnion and Aglaothamnion are similar.

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

iNaturalist: Callithamnion tetricum at iNaturalist World Species Observations database.

WoRMS: Callithamnion tetricum at World Register of Marine Species. Accepted name: Callithamnion tetricum (Dillwyn) S.F.Gray, 1821. AphiaID: 144530.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Callithamniaceae; Callithamnioideae; Callithamnieae; Callithamnion