Vertebrata lanosa is a filamentous red alga that grows as an obligate epiphyte on Ascophyllum nodosum. The short, cylindrical, cartilaginous fronds form beautiful dense reddish-purple tufts along the ochre colored thalli of their host. Branches of this algae are dichotomous (forming 'y's) with pointed tips. Formerly classified as Polysiphonia lanosa, it lacks the distinctive banded pattern typical of Polysiphonia species. As an obligate epiphyte, Vertebrata lanosa cannot grow except attached to other seaweed species by tiny structures called rhizoids that grow into the tissue of the algal host. Ascophyllum nodosum is the most frequent host, though Vertebrata lanosa is sometimes found on Fucus species such as Fucus vesiculosus as well, so it is abundant where these species thrive.

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Garbary, D.J., Deckert, R.J. & Hubbard, C.B. (2005). Ascophyllum and its symbionts. VII. Three-way interactions among Ascophyllum nodosum (Phaeophyceae), Mycophycias ascophylli (Ascopmycetes) and Vertebrata lanosa (Rhodophyta). Algae 20: 353-361.

In Gaeilge: Craonach, Cúnach triosgar, Cluaisíní, Mileara, Millreacha (Brennan 1950), Olann dhearg (Anon. 1978).

In English: Wrack Siphon Weed (Bunker et al. 2010).

Other names: many tubed gable weed, pompon des ascophylles; previously known as Polysiphonia lanosa.

Basionym: Fucus lanosus Linnaeus

Type locality: ‘In Oceano Islandico’ (Iceland)LINN 1274.23