Description: Thallus erect to 30 cms or more, membranous, one cell thick and irregularly split.

Habitat: Epiphytic and epilithic in rock pools of the littoral and in the sublittoral also in salt marshes.

Distribution: Probably widespread though not common in the British Isles. Europe: Mediterranean, Spain, France, Baltic, Norway, Faroes, Spitzbergen and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts and Rhode Island. Further afield: Pacific coast of North America 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 cell thick. Turning brown on drying.

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

iNaturalist: Monostroma obscurum at iNaturalist World Species Observations database.

WoRMS: Monostroma obscurum at World Register of Marine Species.