Mycoblastus is a genus of crustose lichens in the family Tephromelataceae.

[3][4] The genus was circumscribed in 1852 by Johannes Musaeus Norman, who selected the widespread Mycoblastus sanguinarius as the type species.

[8] Mycoblastus species produce a grayish-white or greenish-gray crustose thallus that contains a green algal photobiont from the genus Trebouxia.

The apothecia are typically large, hemmispherical, shiny black or dark pigmented, and lack a margin.

There are highly branched and anastomosing paraphyses that form a network around the asci.