Astrothelium megochroleucum
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Division:	Ascomycota
Class:	Dothideomycetes
Order:	Trypetheliales
Family:	Trypetheliaceae
Genus:	Astrothelium
Species:	A. megochroleucum
Binomial name
Astrothelium megochroleucum Aptroot (2016)

Astrothelium megochroleucum is a species of corticolous (bark-dwelling), crustose lichen in the family Trypetheliaceae.^[1] Found in El Salvador, it was formally described as a new species in 2016 by Dutch lichenologist André Aptroot. The type specimen was collected by Harrie Sipman in the El Imposible National Park (Ahuachapán) at an altitude of 1,300 m (4,300 ft); there, it was found in a coffee plantation growing on the smooth tree bark of Leucaena trichandra.^[2]

The lichen has a smooth and somewhat shiny, ochraceous thallus with a cortex and a thin (about 0.1 mm wide) black prothallus line. It covers areas of up to 4 cm (1.6 in) in diameter. The presence of the lichen induces the formation of galls in the host plant; as a consequence, the bark underneath the thallus splits open and forms a callus. Both the thallus and the pseudostroma contain lichexanthone, a lichen product that causes these structures to fluoresce yellow when lit with a long-wavelength UV light.^[2] The combination of characteristics of the lichen that distinguish it from others in Astrothelium are its prominent, whitish, pseudostromatic ascomata, and the dimensions of its ascospores (60–70 by 16–18 μm).^[3] These spores have three septa, a character that separates it from the otherwise similar Astrothelium ochroleucoides.^[2]

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