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