Astrothelium testudineum is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae.

Astrothelium testudineum is most similar to A. leioplacum, but it can be distinguished by its hamathecium inspersion and larger ascospores.

[2] The thallus of Astrothelium testudineum is thickly corticate, smooth, somewhat shiny, continuous, and ochraceous, covering areas up to cm in diameter.

[2] Ascomata are pyriform, measuring 0.5–0.9 mm in diameter, and are mostly aggregated in groups of 2–6, immersed in the thallus, without pseudostroma.

Asci contain 8 ascospores, which are hyaline, densely muriform, broadly ellipsoid, and measure 50–65 by 23–27 μm.