Description: Thallus erect to 25 cms long and terete. Branches polysiphonous with 4 pericentral cells with cortication in the older branches. Attached by discoid holdfast and clusters of rhizoids. Cystocarps ovoid becoming globular.

Habitat: Common. Epilithic, epiphytic and also on artifical surfaces. Low littoral to 10 m or more.

Distribution: Widespread around the British Isles including Shetlands. Europe: Atlantic coast of France, Netherlands, Denmark, Baltic Sea and Norway. Further afield: Arctic Sea and Canary Islands.

Similar Species: Other species of Polysiphonia are similar and difficult to distinguish.

Key Identification Features:

• 4 pericentral cells, if corticate only at the base, cystocarps ovoid.

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

iNaturalist: Polysiphonia fibrillosa at iNaturalist World Species Observations database.

WoRMS: Polysiphonia fibrillosa at World Register of Marine Species.