Acanthothecis submuriformis 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 M.Cáceres. The type specimen was collected from the Parque Natural Municipal (Porto Velho, Rondônia); here the lichen was found growing on tree bark in primary rainforest.
It has a smooth, ochraceous white thallus lacking a cortex and lacking a prothallus. Its asci are 8-spored, and its ascospores are hyaline, measuring 29–31 by 6–8 μm. The specific epithet refers to the submuriform (somewhat chambered) spores; all spores have between 7 and 9 transverse septa, but of the 8 spores in the ascus, only about 2 have a longitudinal septum.
Acanthothecis submuriformis contains lichexanthone, a lichen product that causes the thallus and ascomata margins to fluoresce yellow when lit with a long-wavelength UV light. This species and Acanthothecis tetraphora are the only species in genus Acanthothecis known to produce lichexanthone.