Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Northern Ireland
Algae/seaweed.
356 species of marine algae have been recorded in the north-east of Ireland. As Counties Londonderry, Antrim and Down are the only three counties of Northern Ireland with a shoreline this will apply to all Northern Ireland. 77 species are considered rare having been recorded rarely.