Description: Thallus of uniseriate filaments, usually unbranched, up to 10 cms long. Forms soft woolly masses. Sometimes attached by basal cell with rhizoids.

Habitat: Common in the upperr littoral in rock pools

Distribution: Widespread around the British Isles. Europe: Mediterranean, Azores, Spain and Portugal, N.France, Faroes, Baltic Sea, Norway and Iceland. Greenland. Atlantic coasts of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New Jersey, Delaware and Virginia. Further afield: the Canary Island, North Pacific from Alaska to California, New Zealand, Japan, South Africa and the subantartic.

Similar Species: Other species of Ulothrix, Urospora and Rhizoclonium, the distinction is microscopic.

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

iNaturalist: Ulothrix flacca at iNaturalist World Species Observations database.

WoRMS: Ulothrix flacca at World Register of Marine Species. Accepted name: Ulothrix flacca (Dillwyn) Thuret, 1863. AphiaID: 145925.

Classification: Biota; Plantae; Viridiplantae; Chlorophyta; Chlorophytina; Ulvophyceae; Ulotrichales; Ulotrichaceae; Ulothrix