Description: Thallus in erect tufts to 20 cms long, much branched. Axes polysiphonous and ecorticate with 9 - 13 (14) pericentral cells and large central cell. Rhizoids cut off from pericentral cells. Cystocarps globular.

Habitat: Common. Epilithic in rock pools and on shells in the low littoral to 20 m.

Distribution: Widely distributed around the British Isles including the Shetlands. Europe: Portugal, Spain, France, Netherlands, Norway and the Faroes. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rode Island, Connecticut and New Jersey.

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

iNaturalist: Polysiphonia nigra at iNaturalist World Species Observations database.

WoRMS: Polysiphonia nigra at World Register of Marine Species.