Description: Microscopic. Monostromatic as discoid irregular patches composed of radiating branching filaments. Red.

Habitat: Lower littoral and sublittoral to 20 m. Epiphytic and epizoic.

Distribution: Ireland: Cos Antrim, Down, Galway and Clare. Scotland: Orkney and Shetlands. England: Devon and Cornwall. Europe: Mediterranean, Portugal, Spain, France, the Baltic, Netherlands, Denmark and Norway. Atlantic coast of North America: arctic Canada, Connecticut, Virginia and North Carolina. Further afield: Arctic Russia, British Columbia to California and Japan. Probably widespread.

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

iNaturalist: Erythrocladia irregularis at iNaturalist World Species Observations database.

WoRMS: Erythrocladia irregularis at World Register of Marine Species.