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  of P. multiforme is not interspersed with oil droplets. The type specimen was collected in Guyana, at the base of , on the bark of a Myrsinaceae tree.

The ascomata of P. multiforme are 0.2–0.3 mm in diameter, with a spherical  that is  and solitary. The ostiole is apical, and the  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.

References

Trypetheliaceae
Lichen species
Lichens described in 2013
Taxa named by André Aptroot
Lichens of Brazil
Lichens of Guyana
Lichens of Venezuela