An order of the class Ascolichenes, also known as the Pyrenolichenes. As now circumscribed, the Pyrenulales includes only those lichens with perithecia that contain true paraphyses and unitunicate asci. Other pyrenolichens with pseudoparaphyses and bitunicate asci have been transferred to the Pseudosphaeriales. The flask-shaped perithecia are uniformly immersed in the medulla of the thalli with a small ostiole opening at the surface. The asci and paraphyses arise from a blackened hypothecium and line the walls of the perithecium. The spores eventually burst the ascal walls and ooze out through the ostiole in a jelly matrix. Details of ascal development have been described rather fully for Dermatocarpon aquaticum. The Pyrenulales are almost all crustose in growth form, with very simple internal structure. The exception is Dermatocarpaceae, large umbilicate species often confused with the typical rock tripe, Umbilicaria, in the Lecanorales.