Astrothelium aenascens is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae. Found in Papua New Guinea, it was formally described as a new species in 2016 by André Aptroot. The type specimen was collected from Varirata National Park (Central Province), where it was found growing on smooth tree bark. The lichen has a smooth and shiny thallus that covers areas of up to 5abbr=onNaNabbr=on in diameter. The species epithet aenascens refers to the lichen's resemblance with Astrothelium aeneum. Thin-layer chromatography shows that the lichen contains an anthraquinone, which the author suggests is probably parietin.