The species is characterized by its large muriform ascospores and is similar in appearance to Astrothelium disjunctum.

The type specimen was collected by the authors from the Sítio Ecológico Buriti on Lago Cujubim (Porto Velho, Rondônia), where it was found growing on tree bark in a disturbed forest.

[2] The thallus of Astrothelium xanthosuperbum is corticate, smooth, shiny, continuous, and olive-green, covering areas up to 3 cm (1.2 in) in diameter.

[2] Ascomata are spherical, measuring 0.4–0.7 mm in diameter, and are solitary or aggregated in groups of 2–6, immersed in pseudostroma.

Thin-layer chromatography reveals the presence of lichexanthone, a lichen product that causes the thallus to fluoresce when lit with a long-wavelength UV light.