Acanthothecis rimosa 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 André Aptroot, Robert Lücking, and Marcela Eugenia da Silva Cáceres. The type specimen was collected from the Pedra Talhada private area in Quebrangulo (Alagoas) at an elevation between . The lichen has a smooth and somewhat shiny, mineral-grey thallus lacking a cortex, and also lacking a surrounding prothallus. The asci contain two spores. The ascospores are hyaline, ellipsoid, and measure 45âÂÂ53 by 13âÂÂ16 üm; they have 15âÂÂ19 transverse and 3âÂÂ4 longitudinal septa. Stictic acid, a lichen product, is found in the lichen and is detectable using thin-layer chromatography.