Notheia anomala is a macroalga in the family Notheiceae and the brown algae order Fucales.

The fronds of Hormosira are weakly attached to the substratum and there is frequent dislodgement in storm events or periods of high wave energy – therefore the fronds that drift may offer long-distance dispersal to Notheia which could be a key mechanism for the distributional success of this species[6] Capon et al. (1998) [7] highlighted for the first time that tetrahydrofurans from Notheia act as potent and selective inhibitors of the larval development of parasitic nematodes, which may be a positive effect that Hormosira receives from this symbiotic relationship.

Notheia has a higher photosynthetic capacity than its host Hormosira, probably because of its greater surface area or smaller allocation to chemical defences.

Although Hormosira is dioecious, Nothiea does not appear to exhibit any preference towards settlement on male or female plants.

Both gametes are pyriform in shape (pear form) with two laterally inserted flagella (the anterior one longer than the posterior).