Pelvetia

Pelvetia canaliculata, channelled wrack, is a very common brown alga (Phaeophyceae) found on the rocks of the upper shores of Europe. It is the only species remaining in the monotypic genus Pelvetia. In 1999, the other members of this genus were reclassified as Silvetia due to differences of oogonium structure and of nucleic acid sequences of the rDNA.

Description

Pelvetia grows to a maximum length of 15 centimetres (6 in) in dense tufts, the fronds being deeply channelled on one side: the channels and a mucus layer help prevent the seaweed drying (desiccation) when the tide is out. It is irregularly dichotomously branched with terminal receptacles, and is dark brown in colour. Each branch is of uniform width and without a midrib. The receptacles are forked at the tips.

It is distinguished from other large brown algae by the channels along the frond. It has no mid-rib, no air-vesicules and no cryptostomata. It forms the uppermost zone of algae on the shore growing at or above high-water mark. The reproductive organs form swollen, irregularly shaped receptacles at the end of the branches. The conceptacles are hermaphrodite and borne within the receptacles.