Description: Thallus up to 20 cms or more, membranous and one cell thick. Deviding irregularly into lobes.

Habitat: Common. Epiphytic and epilithic in the littoral and upper sublittoral fringe including estuaries. May be free-floating.

Distribution: Widespread around the British Isles. Europe: Mediterranean, Portugal, France, Netherlands, Germany, Denmark, the Baltic, Sweden, Norway and Iceland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New Jersey, Maryland, South Carolina, Virginia and Florida. Further afield: British Columbia to California and Japan

Similar Species: Ulva, however the thallus of all species of Monostroma is one cell thick. Enteromorpha is in general tubular and bounded by a membrane one cell thick which may split or become compressed and appear to be two cells thick.

Key Identification Features:

• Membranous, one celled thick.

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

iNaturalist: Monostroma oxyspermum at iNaturalist World Species Observations database.

WoRMS: Monostroma oxyspermum at World Register of Marine Species.