Found in Brazil, it resembles Astrothelium aeneum but differs in several key aspects, including the absence of pigment on the thallus and specific features of its ascospores.

The type specimen was collected on the southern slope of the Serra de Itabaiana National Park, Sergipe, Brazil, at an elevation of approximately 400 m (1,300 ft), on the bark of a tree.

[2] The thallus of Viridothelium leptoseptatum is corticate, smooth, somewhat shiny, and continuous, covering areas up to 5 cm (2 in) in diameter and approximately 0.2 mm thick.

[2] The thallus surface of Viridothelium leptoseptatum is UV negative, and the thallus medulla does not react to a solution of potassium hydroxide (K−); the pseudostroma surface is UV+ (pink to orange), with pigmented parts reacting K+ (blood red) Thin-layer chromatography analysis indicates the presence of an anthraquinone substance, probably parietin.

[2] This species is found on the smooth bark of trees in the Atlantic Forest and, at the time of its initial publication, was known only to occur in Brazil.