Astrothelium xanthosuperbum

The thallus of Astrothelium xanthosuperbum is corticate, smooth, shiny, continuous, and olive-green, covering areas up to 3 cm (1.2 in) in diameter. It is less than 0.1 mm thick and surrounded by a dark black prothallus line, about 0.3 mm wide. The lichen induces gall formation on the host bark, making the bark pieces slightly concave and thickened along the cracks so that they are almost flaking off.^[2]

Ascomata are spherical, measuring 0.4–0.7 mm in diameter, and are solitary or aggregated in groups of 2–6, immersed in pseudostroma. Pseudostromata are black and raised above the thallus. The wall is black all around, up to about 50 μm thick. Ostioles are apical, flat, dark brown, and often surrounded by a pale brown ring. Asci contain 8 ascospores, which are hyaline, muriform, ellipsoid, and measure 130–160 by 28–35 μm.^[2]

In terms of standard chemical spot tests, the thallus surface is UV+ (yellow), and the thallus medulla is K−. Thin-layer chromatography reveals the presence of lichexanthone, a lichen product that causes the thallus to fluoresce when lit with a long-wavelength UV light.^[2]

Astrothelium xanthosuperbum is found on the smooth bark of trees in disturbed rainforests. The species is currently known only from Brazil.^[2]