Polyides rotundus (Hudson) Greville

Polyides rotundus

Description: Thallus erect and terete attached by discoid holdfast and rising up to 20 cms long. Dichotomous branches dividing 5 or 6 times.

Habitat: Common. Epilithic in mid to low water rock pools, often with the holdfast burried in sand, and in the sublittoral to 12 m.

Distribution: Generally distributed around the British Isles from the Shetlands to the Channel Islands. Europe: Portugal, Spain, France, the Baltic, Norway and the Faroes. Atlantic coast of North America: Labrador to Connecticut. Further afield: Arctic Sea.

Similar Species: Furcellaria lumbricalis is similar, the most obvious difference being the holdfast which in Polyides is a discoid crust while in Furcellaria it is branching. Encrusting epiphytes are rare on Polyides but common on Furcellaria.

Key Identification Features:

• Terete frond, dichotomous branching, discoid holdfast.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

WoRMS: Species record : World Register of Marine Species.

iNaturalist: Species account : iNaturalist World Species Observations database