We describe Pyrenula cascadensis as a new species from Washington, U.S.A. It is similar to other Pyrenula from the Pacific Northwest in having 3-distoseptate, faintly pale-brown spores. However, it lacks a lichenized thallus and occurs in montane to subalpine forests. We compare the new species with other Pyrenula species and other similar genera. We present a phylogeny of Pyrenulaceae delimiting at least five independent clades in which almost all species are known to occur partially or exclusively in extratropical areas. The phylogeny shows P. cascadensis forms an isolated clade that is close to, but separate from, a well-supported clade that contains the North American and European species P. coryli, P. laevigata and P. occidentalis. This suggests the possibility of an independent loss of lichenization between P. cascadensis and P. coryli. Keywords: Cascade Mountains, lichen systematics, Mycoglaena, Naetrocymbe, pyrenocarpous fungi, Washington.