Astrothelium trematum is a species of corticolous (bark-dwelling), crustose lichen in the family Trypetheliaceae,[1] first described in 2018.

Found only in Brazil, it is characterised by its lack of lichexanthone and pigments, and distinctive ascospores.

The type specimen was collected near Caraguatatuba, São Paulo, Brazil, in a plantation of Theobroma cacao.

The pseudostroma is low hemispherical, almost completely covered by a thallus layer, about 1–1.5 mm in diameter, and without pigmentation.

[2] Astrothelium trematum was found on tree bark in a cocoa plantation, and at the time of its original publication, was known only to occur in Brazil.