Description: Growing as tufted filaments, monosiophonous or polysiphonous, erect to over 7 cms long with dense branching, opposite or whorled.

Habitat: Not uncommon. Usually epiphytic in the lower littoral.

Distribution: Widely distributed around the British Isles from the Shetlands to Cornwall. Europe: France, Baltic Sea, Norway, the Faroes, Spitzbergeb and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire and Massachusetts. Further afield: White Sea in the Arctic.

Similar Species: Many filamentous brown algae are similar and microscopic examination is required for identification.

Key Identification Features:

• Polysiphonous in older parts but with monosiphonous branches. Branches opposite or whorled.

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

iNaturalist: Isthmoplea sphaerophora at iNaturalist World Species Observations database.

WoRMS: Isthmoplea sphaerophora at World Register of Marine Species.