Astrothelium megochroleucum

{{Short description|Species of lichen}}

{{Use British English|date=November 2022}}

{{Use dmy dates|date=November 2022}}

{{Speciesbox

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| taxon = Astrothelium megochroleucum

| authority = Aptroot (2016)

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Astrothelium megochroleucum is a species of corticolous (bark-dwelling), crustose lichen in the family Trypetheliaceae. 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 {{convert|1300|m|ft|abbr=on}}; there, it was found in a coffee plantation growing on the smooth tree bark of Leucaena trichandra.

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 {{convert|4|cm|in|abbr=on}} 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 {{lichengloss|pseudostroma}} contain lichexanthone, a lichen product that causes these structures to fluoresce yellow when lit with a long-wavelength UV light. The combination of characteristics of the lichen that distinguish it from others in Astrothelium are its prominent, whitish, {{lichengloss|pseudostroma|pseudostromatic}} ascomata, and the dimensions of its ascospores (60–70 by 16–18 μm). These spores have three septa, a character that separates it from the otherwise similar Astrothelium ochroleucoides.