Astrothelium tetrasporum is a species of corticolous (bark-dwelling), crustose lichen in the family Trypetheliaceae,[1] first described in 2016.

Astrothelium tetrasporum was formally described by lichenologists by the André Aptroot and Marcela Eugenia da Silva Cáceres in 2016.

The type specimen was collected near Pousada Mandala on SP-254 in Botucatu, São Paulo, Brazil, at an elevation of about 850 m (2,790 ft), on 9 September 2012.

[2] The thallus of Astrothelium tetrasporum is corticate, discontinuous, and consists of sinuose to moniliform rows of spherical to slightly flattened bullate areas.

When the spores are young, they have a markedly thickened median septum with two polar gelatinous caps approximately 5 μm thick.