Description: Thallus erect to 10 cms long, polysiphonous and terete. Much branched with 4 pericentral cells, cortication absent or only near holdfast. Cystocarps globular.

Habitat: Epiphytic and on rocks and artifical surfaces in the low littoral.

Distribution: British Isles: south and east England, Wales, Ireland and the Channel Islands. Europe: France, Netherlands, Helgoland, Denmark and Norway. Atlantic coast of North America: from Canada to South Carolina. Further afield: the Canary Islands.

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

iNaturalist: Polysiphonia harveyi at iNaturalist World Species Observations database.

WoRMS: Polysiphonia harveyi at World Register of Marine Species. Accepted name: Melanothamnus harveyi (Bailey) Díaz-Tapia & Maggs, 2017. AphiaID: 1027787.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Rhodomelaceae; Polysiphonieae; Polysiphonia