Acanthothecis subfarinosa is a species of corticolous (bark-dwelling) lichen in the family Graphidaceae.

Found in Brazil, it was formally described as a new species in 2022 by Shirley Cunha Feuerstein.

The type specimen was collected from remnant cerrado in Campo Mourão (Paraná).

The asci contain 8 spores; the ascospores are hyaline, measuring 22–30 by 5 μm with 6 to 8 transverse septa.

Acanthothecis subfarinosa contains norstictic acid, a lichen product that is detectable using thin-layer chromatography.