Description: Thallus erect to 10 cms, a membrane one celled thick splitting into broad elongate segments.

Habitat: Frequent. Rock pools of the littoral, epiphytic and epizoic on mollusc shells also sublittoral.

Distribution: Widely distributed in the North Atlantic. Generally around the British Isles. Europe: France, Netherlands, Baltic Sea, Norway, Faroes and Iceland. Atlantic coast of North America: Canada to New Jersey. Further afield: Arctic Seas from Murman Sea, the White Sea to the west coast of Greenland, Alaska to California and Argentina.

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:

• Mambranous, one cell thick.

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

iNaturalist: Monostroma grevillei at iNaturalist World Species Observations database.

WoRMS: Monostroma grevillei at World Register of Marine Species. Accepted name: Monostroma grevillei (Thuret) Wittrock, 1866. AphiaID: 145940.

Classification: Biota; Plantae; Viridiplantae; Chlorophyta; Chlorophytina; Ulvophyceae; Ulotrichales; Monostromataceae; Monostroma