Ascoseira is a monotypic genus of seaweed in the brown algae (class Phaeophyceae).

[3][4] The single and type species, Ascoseira mirabilis Skottsberg, is a large parenchymatous macroalgae, and is endemic to the Antarctic Ocean.

[5] Ascoseira is assigned to its own order.

[3][6] The alga grows in subtidal waters at depths of from 3 to 15 meters.

This Phaeophyceae (or brown alga) article is a stub.