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.
Ascoseira
Ascoseira is a monotypic genus of seaweed in the brown algae (class Phaeophyceae). The single and type species, Ascoseira mirabilis Skottsberg, is a large parenchymatous macroalgae, and is endemic to the Antarctic Ocean. "Ascoseira" is assigned to its own order. The alga grows in subtidal waters at depths of from 3 to 15 meters.