Vertebrata lanosa (Linnaeus) T.Christensen

Also known as Polysiphonia lanosa (Linnaeus) Tandy
Common name: Olann Dhearg (Irish).
Description: Cartilaginous, cylindrical, densely tufted, dark reddish-purple fronds, to 75 mm long, attached by creeping rhizoids with branches penetrating the host fronds of Ascophyllum nodosum. Repeatedly pseudodichotomously branched, apices pointed, widely forked. Large central siphon with 12-24 pericentral siphons, ecorticate, articulations shorter than broad.
Habitat: Hemiparasitic on Ascophyllum nodosum, more rarely on Fucus vesiculosus, never on rock (appearances can be deceptive as it can grow on old stalks of both species) in the sheltered midtidal, generally distributed, usually abundant where Ascophyllum occurs.Vertebrata is gnerally infected with a tiny, more or less colourless parasitic red alga called Choreocolax polysiphoniae, to which it is closely related.

Link: Algaebase

Species list

Photograph © M.D. Guiry