Description: The gametangial phase is of fronds growing from a crustose base to 35 cms long, repeatedly branched and tapering at both ends, hollow and gelatinous. The tetrasporangial phase is encrusting and quite unlike the gametangial phase.

Habitat: Rare. Epilithic in shallow pools of the lower littoral and sublittoral to 5 m.

Distribution: Widely distributed around the British Isles including the Shetlands and Channel Islands. Europe: Mediterranean, Portugal, Spain, France, Netherlands, Baltic, Norway and Iceland. Atlantic coast of North America from Newfoundland to Connecticut. Further afield: both sides of the north Pacific.

Similar Species: The gametangial phase resembles Lomentaria clavellosa .

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

iNaturalist: Gloiosiphonia capillaris at iNaturalist World Species Observations database.

WoRMS: Gloiosiphonia capillaris at World Register of Marine Species. Accepted name: Gloiosiphonia capillaris (Hudson) Carmichael, 1833. AphiaID: 145232.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Gigartinales; Gloiosiphoniaceae; Gloiosiphonia