Astrothelium lucidothallinum

{{Short description|Species of lichen}}

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

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

{{Speciesbox

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| taxon = Astrothelium lucidothallinum

| authority = Aptroot (2016)

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Astrothelium lucidothallinum is a species of corticolous (bark-dwelling), crustose lichen in the family Trypetheliaceae. Found in Guyana, it was formally described as a new species in 2016 by Dutch lichenologist André Aptroot. The type specimen was collected about {{convert|30|km|mile|abbr=on}} south of Aishalton (Upper Takutu-Upper Essequibo) at an altitude of {{convert|300|m|ft|abbr=on}}; there, it was found in a savanna growing on smooth tree bark. The lichen has a smooth and somewhat shiny, pale yellowish grey thallus with a cortex and a thin (0.1 mm wide) black prothallus line. It covers areas of up to {{convert|9|cm|in|abbr=on}} in diameter. The thallus contains lichexanthone, a lichen product that causes it 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: the presence of lichexanthone only in the thallus; the indistinctly pseudostromatic ascomata, with {{lichengloss|erumpent}} pseudostromata—whitish in colour but lacking a sharp outline; and the dimensions of the ascospores (70–90 by 18–20 μm) as well as their number per ascus (eight).