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.
Himanthalia elongata
Himanthalia elongata is a brown alga (class Phaeophyta or Phaeophyceae) in the order Fucales, also known by the common names thongweed, sea thong and sea spaghetti. It is found in the north east Atlantic Ocean and the North Sea.