Agyrium

Agyrium was first proposed by Elias Magnus Fries in his 1821 work Systema Mycologicum,[3] although the name was not published validly as a type species was not indicated;[4] Fries published the name validly a year later in the second volume of the same work.[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.[7] This is a condition that has been described as "facultative parasitism".[8]

As of May 2021, Species Fungorum accepts two species of Agyrium.

• Agyrium aurantium W.Y.Zhuang & Zhu L.Yang (2006)
• Agyrium rufum (Pers.) Fr. (1822)

The type species, Agyrium rufum, has a largely Northern Hemisphere distribution and occurs widely in Europe, although it has also been recorded in Tasmania.[7] Agyrium aurantium occurs in China.[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. Several of them have since been transferred to other genera. For example:

• Agyrium caesium Fr. (1822) = Puttea caesia
• Agyrium densum Fuckel (1871) = Mellitiosporiella densa
• Agyrium flavescens Rehm (1903) = Skyttella mulleri
• Agyrium nigricans Fr. (1822) = Platygloea nigricans
• Agyrium nitidum Lib. (1834) = Agyriella nitida
• Agyrium phragmiticola Hansf. (1946) = Neottiosporina phragmiticola
• Agyrium solidaginis (Ces.) De Not. (1863) = Ploettnera solidaginis
• Agyrium vulpinum (Tul.) H.Olivier = Phacopsis vulpina