Pyrenula guyanensis

About

Pyrenula guyanensis is a species of corticolous (bark-dwelling) crustose lichen in the family Pyrenulaceae. The species forms a pale yellowish-gray crust with a slightly warted surface and produces dark fruiting bodies (perithecia) in distinct warts up to 1.2 mm wide. It contains lichexanthone, a substance that causes the thallus to fluoresce yellow under ultraviolet light, and grows on tree bark in low open woodlands and savannah scrub on nutrient-poor sandy soils.

Summary from Wikipedia