Description: Thallus to 60 cms long, attached by irregular holdfast. Well branched, the base of branches not swollen as in C.nodicaulis. Secondary latteral branches flattened with midrib and serrated margin. Older branches are naked at the base, cartilaginous and slender containing small elliptical air-vesicles (aerocysts), about 3 - 4 mm, below the dichotomies.

Habitat: Uncommon. Epilithic in rock pools near low water.

Distribution: Generally south western, recorded from the south and west coasts of Ireland and the south west coast of England, the Channel Islands. Europe: Portugal, Atlantic coast of Spain and France. Further afield: Salvage Islands, Canary Islands, Mauritania, Senagal and Cape Verde Islands.

Similar Species: Other species of the genus.

Key Identification Features:

• Base of branches not swollen but with aerocysts, not found in winter, beneath a dichotomy. Not iridescent underwater.

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

iNaturalist: Cystoseira foeniculaceus at iNaturalist World Species Observations database.