Caulacathus ustulatus (Turner) Kützing
Also known as Caulacanthus okamurae Yamada
Description: Densely tufted, dark purple to brownish, cartilaginous fronds, to 30 mm long, profusely and irregularly branched, narrowing fairly abruptly towards the apices giving a horn-like appearance. Attached by creeping stolons producing multicellular rhizoids.
Habitat: On rock, on mussels and epiphytic, intertidal, on exposed shores.
Distribution: Atlantic populations from Biarritz south to Spain, Portgual and the Azores. Pacific populations widely distributed in China, Japan, the Philippines and Australia. Potentially adventive populations in England, NW France and S California and Washington State.
Notes: Caulacanthus ustulatus was first described from Biarritz on the Atlantic coast of France and this was the known northern limit of the species for many years. In recent years, Caulacathus was reported from Brittany (Roscoff) and was later found in SW Britain. However, molecular studies of populations worldwide have indicated that at least two entites are present and that the recently found populations of Caulacanthus in Brittany and SW England probably represent an adventive species from the Pacific.
Photographs: intertidal mussel bed south of Godrevy Point, Gwithian, near Hayle, Cornwall; 27 September 2014, David Fenwick © David Fenwick, Snr.
Photographs © M.D. Guiry