It was first formally described as a new species in 1852 by Italian botanist Abramo Bartolommeo Massalongo, as Lecidea thallicola.

[4] The known generic hosts of Phacopsis thallicola are all in the Parmeliaceae: Parmotrema, Cetrelia, Flavopunctelia, and Hypotrachyna.

[5] Some historical synonyms of Phacopsis thallicola have resulted from proposed taxonomic transfers from its original genus Lecidea to the genera Scutula, Mycoblastus, and Nesolechia.

[1] Abrothallus curreyi, first reported by William Lauder Lindsay from New Zealand in 1866, is a synonym of Phacopsis thallicola.

[2][5] Characteristics of Phacopsis thallicola include its dark-brown hypothecium (the area of tissue in the apothecium immediately below the subhymenium), and the mostly sessile, marginate apothecia.