Description: Growing to form small spots less than I mm in diameter on hosts. Prostrate base of monostromatic branching filaments and erect short filaments rising from an inner disc.

Habitat: Common. Epiphytic on Dumontia in the lowlittoral and sublittoral.

Distribution: Widely distributed in the British Isles. Europe: Netherlands, Denmark, Baltic Sea, Sweden and Norway. Atlantic coast of North America: Canada and Maine.

Similar Species: Myrionema

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

iNaturalist: Ulonema rhizophorum at iNaturalist World Species Observations database.

WoRMS: Ulonema rhizophorum at World Register of Marine Species.