[2] Originally created in 1909 but long unused, the genus was revived in 2020 to accommodate D. spadicea when molecular studies showed this species fell outside the main Arthonia clade.

The species grows as a thin, greyish to greenish crust beneath tree bark, producing small black disc-like reproductive structures (apothecia) that resemble drops of tar.

[4] In 1981, D. lurida was formally rejected following a nomenclatural proposal by David Hawksworth and Martha Sherwood to protect the later name Arthonia spadicea Leight.

DNA analysis has suggested that Arthothelium norvegicum may also belong in Diarthonis, though further research is needed to confirm this relationship due to long phylogenetic branch lengths.

[4] The genus also produces smaller reproductive structures called pycnidia, which are brown with orange to reddish-brown walls that also turn pale purple with potassium hydroxide.

[4] Diarthonis spadicea is considered an indicator species of good habitat quality and ecological continuity in broadleaved woodlands dominated by Quercus robur.