[5] The species Agyrium rufum was assigned as the type by Frederic Clements and Cornelius Lott Shear in 1931.

[6] Characteristics of genus Agyrium include the following: a poorly developed thallus that is immersed in its substrate; ascomata in the form of an apothecium with a reduced ring-shaped exciple (the layer surrounding the hymenium that sometimes develops into a distinct margin); paraphyses that are highly branched; and ascospores that are ellipsoid and thin-walled.

[7] The mycelia of Agyrium fungi, although not strictly lichenised, are associated with and sometimes penetrate green algae – particularly near the apothecia.

The type species, Agyrium rufum, has a largely Northern Hemisphere distribution and occurs widely in Europe, although it has also been recorded in Tasmania.

[9] Although 46 taxa have been placed in Agyrium since its inception, many of them were described more than a century ago and have not been investigated with modern molecular techniques.