Pyrenula leucostoma is a species of corticolous (bark-dwelling), crustose lichen in the family Pyrenulaceae.
Pyrenula leucostoma is a crustose lichen that has a grey-brown and brown to olive green thallus, and subglobose black ascomata which measure in diameter.
The lichen was formally described as a new species by Swedish botanist Erik Acharius in 1814.
The species is pantropical, found in areas including Southeastern North America, the Caribbean and Australia, in eastern Queensland, New South Wales and on Norfolk Island. It was first recognised as being present in New Zealand in 2015. The species is often found in open, coastal habitats and shaded forests, found on the bark of hardwood trees. In Nepal, P. leucostoma has been reported from 2,400 to 2,600 m elevation in a compilation of published records.