Astrothelium macrostomum

The species was formally described as new to science in 2016 by the Dutch lichenologist André Aptroot. The type collection was made by Harrie Sipman in , Minas Gerais, Brazil, on September 16, 1997. ==Description==

The thallus of Astrothelium macrostomum is , smooth, somewhat shiny, and continuous, covering areas up to 7 cm in diameter and less than 0.1 mm thick. It appears olive-green to olive-grey, typically lacking a , and induces gall formation on the host bark, causing the lower bark or cambium layer to swell and erupt through the upper bark. Ascomata are (pear-shaped), about 0.6–1.2 mm in diameter, usually aggregated in groups of 2–5, and mostly immersed in the bark tissue. The wall is , up to approximately 80 μm thick. Ostioles are eccentric and fused, with a flat, white- appearance, surrounded by a whitish zone. The does not contain oil lobules. Asci each contain eight . These ascospores are hyaline, 5–7-septate, , measuring 65–85 by 16–19 μm, with pointed ends and diamond-shaped , not surrounded by a gelatinous layer. were not observed to occur in this species. ==Chemistry==

The thallus surface of Astrothelium macrostomum is UV−, while the medulla is K−. The ostiolar region has a UV+ (yellow) reaction. Thin-layer chromatography indicates the presence of lichexanthone, a xanthone compound that fluoresces when lit with a long-wavelength UV light. ==Similar species==

Astrothelium macrostomum is similar to Astrothelium eustomum, but can be differentiated by its 5–7-septate , as opposed to the 3–5-septate and smaller ascospores of A. eustomum. Astrothelium diplocarpoides shares some similar characteristics, but differs in having an inspersed and the presence of lichexanthone throughout the thallus. ==Habitat and distribution==

Astrothelium macrostomum grows on the smooth bark of trees within rainforests. It is known to occur in Brazil, Guyana, and Venezuela. ==See also==