Callithamnion tetragonum
- kingdom: Plantae
- phylum: Rhodophyta
- class: Florideophyceae
- order: Ceramiales
- family: Callithamniaceae
- genus: Callithamnion
- species: Callithamnion tetragonum
Yarmouth
Nova Scotia
Canada- France
Tossa de Mar
Catalonia
Spain
Gosport
Ilfracombe
Portsmouth
Sidmouth
Swanage
Weymouth
England
United Kingdom
East Falmouth
Oak Bluffs
Onset
West Falmouth
Massachusetts
Beaufort
North Carolina
Newport
Rhode Island
United States
Roscoff
Madalena