[1] Found in Brazil, it was formally described as a new species in 2016 by lichenologists André Aptroot and Marcela Cáceres.

The species is closely related to Astrothelium ceratinum but differs in its ascospore size.

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

[2] Ascomata are spherical, measuring 0.3–0.5 mm in diameter, and appear solitary or in groups of 2–4, erumpent from the bark.

[2] Astrothelium solitarium is found on smooth bark of trees in primary forests.