Description: Thallus in dense tufts of ecorticate axes erect to 10 cms long. Branching alternately in one plane. Tetrasporangia sessile and latteral not terminal.

Habitat: Epiphytic, epilithic and epizoic. Littoral and sublittoral to 10 m.

Distribution: British Isles: common on the south coasts of England and Wales and recorded from Northern Ireland and Scotland. Europe: Mediterranean, Portugal, Atlantic coasts of Spain and France, Baltic Sea and Norway.

Similar Species: Species of Aglothamnion and Compsothamnion thuyoides.

Key Identification Features:

• Tetrasporangia sessile and lateral.

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

iNaturalist: Compsothamnion gracillimum at iNaturalist World Species Observations database.

WoRMS: Compsothamnion gracillimum at World Register of Marine Species.