Description: Thallus small , monosiphonous, erect in tufts to 1.5 cm long, branching pseudodichotomously in whorls of 4 on the axis.

Habitat: Epiphytic and epizoic from low littoral to 10m sublittoral.

Distribution: British Isles on southwestern coasts: Ireland, Wales, England, Isle of Man and the Channel Islands. Europe: Mediterranean and Spain to the Netherlands. Further afield: Canary Islands.

Similar Species: Pterothamnion plumula.

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

iNaturalist: Pterothamnion crispum at iNaturalist World Species Observations database.

WoRMS: Pterothamnion crispum at World Register of Marine Species. Accepted name: Pterothamnion crispum (Ducluzeau) Nägeli, 1862. AphiaID: 144682.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Ceramiaceae; Ceramioideae; Pterothamnieae; Pterothamnion