Astrothelium aeneoides

Astrothelium aeneoides has an olive-green to olive-grey, smooth and somewhat shiny thallus up to 8 cm (3.1 in) in diameter and about 0.2 mm thick. Its ascomata are immersed in the thallus; they are spherical, measuring 0.7–1.0  mm in diameter and arranged in groups of 2 to 5. They are contained in structures called pseudostromata (resembling a perithecium but containing both fungal tissue and substrate tissue) that have a raised surface texture distinct from that of the surrounding thallus. The ascospores, which number eight per ascus, are hyaline, spindle-shaped (fusiform) with rounded ends, have 3 septa, and measure 20–25 by 6–9 μm. The internal chambers formed by the septa (the lumina) are diamond shaped. The use of thin-layer chromatography reveals the presence of a lichen product that the author suggests is parietin. The expected results of standard chemical spot tests are: thallus surface UV−, thallus medulla K−; pseudostroma surface UV+ (pink to orange), medulla of pseudostroma K+ (blood red).^[2]

Astrothelium aeneum is similar in morphology; A. aenoides differs by a lack of orange pigment on the thallus. Another similar species, A. aenascens, is distinguished from A. aenoides by the presence of an inspersed hamathecium.^[2] Astrothelium flavostromatum is another lookalike that is distinguished by a strongly convex and swollen (bullate) thallus and a cream-coloured pseudostromata.^[3]

• List of lichens of Brazil