Plocamium cartilagineum (Linnaeus) Dixon

Plocamium cartilagineum

Description: Thallus grows from a discoid holdfast to form a frond with distinctive pectinate branching. The frond, up to 15 cms long, is generally flattened and the profuse sympodial branching. The final branchlets are comb-like in groups of 2 - 6 in regular sequence, each group alternating with a similar group on the other side. Gametangial and tetrasporangial plants are similar.

Habitat: Common. Epilithic and epiphytic in the lower littoral and sublittoral to 30 m or more.

Distribution: All around the British Isles including the Shetlands. Europe: Mediterranean, Azores, Portugal, Atlantic coast of Spain and France, Norway, Faroes and Iceland. Further afield: Pacific America from Alaska to California, Chile and the Galapagos Islands, Canary Islands and Australia. Widespread in temperate seas.

Similar Species: Sphaerococcus coronopifolius and Callophyllis cristata are similar but do not show the distinctive branching pattern. Recent studies have shown that there are actually four species of Plocamium in Northern Europe, P. cartilagineum, Plocamium subtile, Plocamium nanum and Plocamium maggsiae (Saunders & Lehmkuhl, 2005).

Key Identification Features:

• Easily recognised by the "comb-like" final branchlets.

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