Description: The gametangial phase grows from a discoid holdfast, branching dichotomously to a maximum of 17 cms. The frond is channelled often with reproductive papillae. The tetrasporic phase grows as a crust up to 5 cms in diameter.

Habitat: Epilithic from mid littoral rock pools to the upper sublittoral. One of the most common marine algae.

Distribution: All around the British Isles. Europe: Portugal, Spain, Netherlands, Norway, Faroes and Iceland, the most northerly record is Gjesvaer near the North Cape of Norway. Greenland. Atlantic coast of North America from Labrador to Connecticut. Further afield: Arctic Sea from Baffin Bay, Canary Islands.

Similar Species: The gametangial phase of Mastocarpus is similar to Chondrus crispus however Mastocarpus is readily distinguished by the channelled frond and often with the reproductive cystocarps. The tetrasporic phase is more difficult to identify.

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

iNaturalist: Mastocarpus stellatus at iNaturalist World Species Observations database.

WoRMS: Mastocarpus stellatus at World Register of Marine Species. Accepted name: Mastocarpus stellatus (Stackhouse) Guiry, 1984. AphiaID: 145650.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Gigartinales; Phyllophoraceae; Mastocarpus