Cyphellostereum georgianum is a corticioid basidiolichen first described inâ¯2019 from the coastal plain of Georgia, USA. A member of the family Hygrophoraceae, it sits within the Dictyonema clade, a group of lichens that partner a basidiomycete fungus with filamentous cyanobacteria. Its closest relative is the SouthâÂÂCarolinian C. jamesianum, but the two differ markedly in thallus texture and color.
The species was formally named and described by Manuela Dal Forno, R. Troy McMullin, and Robert Lücking. The holotype was collected on March 29,â¯2013 in Harper Lake Park (McIntosh County, Georgia) where it formed a mat on the trunk of a deciduous tree at 25 m elevation. Molecular data (ITS rDNA) place C. georgianum in a wellâÂÂsupported lineage inside the genus Cyphellostereum and sister to C. jamesianum. The genus itself is nested in tribe Arrheniae of Hygrophoraceae, a lineage otherwise dominated by nonâÂÂlichenised agarics.
The lichen produces a crustoseâÂÂfilamentous thallus: a thin, firmly attached crust made of countless intertwined cyanobacterialâÂÂfungal threads. At its base the thallus forms a continuous darkâÂÂgreen carpet; above this are irregular, slightly raised patches where the threads are packed more densely, giving a yellowâÂÂgreen tinge.
Under the microscope each thread (called a fibril) consists of a chain of cyanobacterial cells 7âÂÂ12.5 üm wide sheathed by branched fungal hyphae. Occasional paleâÂÂyellow heterocytesâÂÂspecialised nitrogenâÂÂfixing cellsâÂÂpunctuate the filaments. Clamp connections on the fungal hyphae confirm its basidiomycete identity.
Reproduction occurs on the underside of the lichen where tiny, white, crustâÂÂlike pads (the hymenophores) develop. These corticioid basidiocarps can reach 14 mm long but remain only about 2 mm across. In section the fertile layer is up to 100 üm thick and built of 2âÂÂ4 üm hyphae; immature clubâÂÂshaped structures (basidioles) measure 3âÂÂ4â¯ÃÂâ¯12âÂÂ18 üm. Mature basidia and basidiospores have not yet been observed.
Microscopically, C. georgianum builds a darkâÂÂgreen crust of densely tangled fibrils that rise into thick, moundâÂÂlike patches, whereas its sister species C. jamesianum spreads as a much looser layer of individual to only slightly interwoven fibrils. C. jamesianum is also thinner and more bluish, with clearly separated, sometimes yellowâÂÂtinged fibrils, and it lacks the elevated patches that give C. georgianum its mottled texture.
As of its original publication, Cyphellostereumâ¯georgianum is known only from the type locality in Harper Lake Park, Georgia, where it grows on the bark of live hardwoods such as oaks within a lowâÂÂlying pineâÂÂoak woodland. The surrounding canopy is dominated by Pinus taeda with a mixed midâÂÂstorey of Quercus hemisphaerica, Q. geminata, Ilex opaca and other broadâÂÂleaved species; shrubs include saw palmetto and various blueberries. The lichen overgrows bark and adjacent bryophyte mats in humid, shaded microhabitats but has not been recorded outside this site.