Description: Thallus of uniseriate filaments, microscopic or very small, no more than 0.5 mm long. Growing from an endophytic base which branches when the filaments emerge. Appearing as a red felt when dry.

Habitat: Filaments grow from between the host filaments. On Ralfsia and molluscs in the midlittoral and lowerlittoral.

Distribution: England: Cos Dorset, Devon, Cornwall. Scotland: Fife. Ireland: Co. Mayo. Channel Islands. Further afield: South Africa and the Pacific coast of North America.

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

iNaturalist: Erythrotrichia welwitschii at iNaturalist World Species Observations database.

WoRMS: Erythrotrichia welwitschii at World Register of Marine Species.