Lithothelium fluorescens

Lithothelium fluorescens is a species of corticolous (bark-dwelling), crustose lichen in the family Pyrenulaceae. It is known from montane rainforest sites in Puntarenas Province, Costa Rica, where it was collected on bark on the lower trunk. The lichen is identified mainly by microscopic characters in its flask-shaped fruiting bodies (perithecia) and ascospores, rather than by any obvious surface features. The thallus is ochraceous and has a cortex, and the perithecia are mostly immersed but show as small, hemispherical warts. In standard lichen spot tests, the thallus fluoresces yellow under ultraviolet light, and it contains the lichen substance lichexanthone. ...read more on Wikipedia.