The genus Pyrenula consists of crustose lichens that usually grow on smooth, shaded bark. About 750 taxa have been named in the genus, although the majority of these names have been excluded from the genus as they have been transferred to other genera, or are considered synonyms. In his world key to the Pyrenula species, published in 2012, André Aptroot accepted 169 species, including 7 not yet formally described. As of March 2022, Species Fungorum accepts 168 species of Pyrenula.