Compositrema

fruiting bodies with a stroma made of both thallus tissue and bits of host tissue), which sets it apart from the otherwise similar genus Stegobolus

Phylogenetically, Compositrema is closely akin to Stegobolus but is genetically quite distant, forming a strongly supported clade that is a distant relative of the Myriotrema album group.^[4] Compositrema is in the tribe Ocellularieae of the subfamily Graphidoideae in the Graphidaceae.^[5] Two species were initially included in this genus,^[4] and two others added in 2014.^[6]

isidia are present on these lichens. The photobiont layer contains scattered clusters of calcium oxalate crystals among its cells. The apothecia, or the reproductive parts of the lichen, are grouped into distinct pseudostromata, which are rounded to angular and can be either erumpent or sessile. The disc-like part of these pseudostromata is pale brown and dusted with a thin white pruina. On a more microscopic level, Compositrema lichens have unbranched paraphyses, and each ascus contains eight ascospores that are ellipsoid in shape with thick septa and lens-shaped lumina. These ascospores range from colourless to pale brown and react with iodine to give a violet-blue colour. Psoromic acid is a secondary metabolite (lichen product) that occurs in Compositrema.^[4]