Description: Thallus large to 50 cms long, tubular and hollow but narrow, cells in 3 to 12 longitudinal and transverse rows. Branched or unbranched, diameter more or less the same throughout though tapering at base. Forming a tangled mass of threads. Majority of cells with one pyrenoid.

Habitat: Common. Epilithic or epiphytic throughout the littoral, also in brackish waters.

Distribution: Widespread around the British Isles. Europe: Azores, Portugal, Ataltic Spain and France, Netherlands, Denmark, Baltic Sea, Norway, Faroes and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut and Long Island, New Jersey, Delaware, Maryland, Virginia and South Carolina. Further afield: Canary Islands, Bermuda, Gulf of Mexico, Jamaica, Caribbean, Brazil, Pacific coast of America from Alaska to Mexico, Perue, South Africa, Australia, Tasmania, New Zealand, Sri Lanca and Japan.

Similar Species: Other species of Enteromorpha may br similar. Microscopic examination required to confirm identification.

Key Identification Features:

• Thallus tubular, cells in rows.

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

iNaturalist: Ulva prolifera at iNaturalist World Species Observations database.

WoRMS: Ulva prolifera at World Register of Marine Species.