Astrothelium tetrasporum

The thallus of Astrothelium tetrasporum is corticate, discontinuous, and consists of sinuose to moniliform rows of spherical to slightly flattened bullate areas. These areas become locally almost like thick squamules, mostly consisting of a hyaline cortex up to 230 μm thick, somewhat shiny, covering areas up to 10 cm in diameter, and are olive-green in colour. Ascomata are pyriform (pear-shaped), measuring 0.7–1.3 mm in diameter, single, and immersed in the thallus. The wall is carbonized and up to 70 μm thick. Ostioles are apical to eccentric, not fused, erumpent, brown, and chimney-like. The hamathecium does not contain oil globules. Asci contain four ascospores each. Ascospores are hyaline, muriform, fusiform, measuring 145–175 by 30–35 μm, with rounded ends. When the spores are young, they have a markedly thickened median septum with two polar gelatinous caps approximately 5 μm thick. Pycnidia were not observed to occur in this species.^[2]

The thallus surface of Astrothelium tetrasporum is UV−, and the medulla does not react to potassium hydroxide (K−). Thin-layer chromatography analysis did not detect any secondary metabolites.^[2]

This species is found on the smooth bark of trees in dry forests, including a forest remnant in a botanical garden. At the time of its original publication, it was known to occur only in Brazil.^[2]