Description: Thallus appearing as small spots on various hosts. Creeping filaments form a disc without erect branches other than colourless hairs exhibiting a considerably elongated basal cell.

Habitat: Apparently rare. Epiphytic on algae and Zostera in the sublittoral to 20 m..

Distribution: Widespread in the British Isles. Europe: Baltic Sea, Norway and Iceland. Greenland. Atlantic coast of North America: Canada. Further afield: the Canary Islands.

Similar Species: There are other small algae appearing as spots or stain-like patches. All difficult to identify and require microscopic examination.

Key Identification Features:

• Numerous characteristic hairs exhibiting a considerably elongated basal cell.

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

iNaturalist: Phaeostroma pustulosum at iNaturalist World Species Observations database.

WoRMS: Phaeostroma pustulosum at World Register of Marine Species.