Description: Thallus filamentous and small in tufts to 2.5 cms long. Prostrate axis spreads over substrate, producing erect axes. Branches irregular or secund.

Habitat: Rare. Epiphytic, epizoic at very low littoral to 20 m,

Distribution: Apparently widespread in British Isles: Dorset, Cornwall, Pembroke, Inverness, Down, Antrim. Europe: Mediterranean, Atlantic coast of Spain and France. Further afield: Morocco.

Similar Species: Spermothamnion repens.

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

iNaturalist: Spermothamnion strictum at iNaturalist World Species Observations database.

WoRMS: Spermothamnion strictum at World Register of Marine Species. Accepted name: Spermothamnion strictum (C.Agardh) Ardissone, 1883. AphiaID: 144704.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Wrangeliaceae; Spermothamnieae; Spermothamnion