Pyrenula infrastroidea is a species of corticolous (bark-dwelling) crustose lichen in the family Pyrenulaceae. The species forms a relatively thick yellowish-gray crust on bark and produces fruiting bodies that are mostly immersed in the thallus, typically occurring in clusters of three to six with fused openings. It is characterized by ascospores that are divided by several cross-walls and occasional lengthwise walls into rounded compartments. The lichen is known only from the Potaro-Siparuni region of Guyana, where it grows on smooth-barked canopy branches in forests and savanna woodlands at elevations around 800 m (2,600 ft).