Description: Thalli erect 1 m or more in length. Main axis slightly flattened to 3 mm wide growing from a discoid holdfast, profuse irregular branching. Ultimate branches are alternate short and spine-like, in spring and early summer young fronds bear short tufts of oppositely branched filaments 4 mm long.

Habitat: Common. Epilithic in lower littoral and sublittoral to 15 m or more.

Distribution: Generally distributed around the British Isles. Europe: Mediterranean, Portugal, Atlantic coasts of Spain and France, Germany, Denmark, Baltic Sea, Sweden, Norway, Faroes and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, Long Island and New Jersey. Further afield: Arctic Seas: Spitzbergen, Murman Sea, White Sea, Kara Sea, Baffin Island and Alaska to Oregon.

Similar Species: D.viridis is similar but with opposite branching. D. ligulata is flattened.

Key Identification Features:

• Slightly flattened axis with alternate spine-like branches.

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

iNaturalist: Desmarestia aculeata at iNaturalist World Species Observations database.

WoRMS: Desmarestia aculeata at World Register of Marine Species. Accepted name: Desmarestia aculeata (Linnaeus) J.V.Lamouroux, 1813. AphiaID: 145307.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Fucophycidae; Desmarestiales; Desmarestiaceae; Desmarestia