Polymeridium multiforme

{{Short description|Species of lichen}}

{{Use dmy dates|date=March 2023}}

{{Speciesbox

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| taxon = Polymeridium multiforme

| authority = Aptroot (2013)

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Polymeridium multiforme is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae. It is found in the Neotropics, with specimens recorded from Brazil, Guyana, and Venezuela. The lichen was described by Dutch lichenologist André Aptroot in 2013. This lichen closely resembles Polymeridium quinqueseptatum, but its thallus is whitish-grey and fluoresces yellow under ultraviolet light (UV+ yellow). Additionally, the {{lichengloss|hamathecium}} of P. multiforme is not interspersed with oil droplets. The type specimen was collected in Guyana, at the base of {{ill|Makarapan Mountain|ceb}}, on the bark of a Myrsinaceae tree.

The ascomata of P. multiforme are 0.2–0.3 mm in diameter, with a spherical {{lichengloss|centrum}} that is {{lichengloss|erumpent}} and solitary. The ostiole is apical, and the {{lichengloss|hamathecium}} features filaments that profusely anastomose. There are eight ascospores per ascus, which are iodine-negative, 4–7-septate, and measure 19–26 by 5–7 μm. The ascospores are not ornamented, and their walls are not thickened. Lichexanthone is present in the lichen's chemistry.