Stigmidium cartilagineae Calatayud &Triebel (on the apothecial discs of Squamarina cartilaginea), a lichenicolous fungus belonging to Stigmidium s. str., is described as new. Two other species of Stigmidium s. 1. with a net of branched and anastomosing, rudimentary interascal filaments are also described as new to science: Stigmidium rouxianum Calatayud & Triebel (on Acarospora cervina) and S. squamarinicola Calatayud & Triebel (on the thallus of Squamarina spp.). They are related to Stigmidium psorae and treated here as ‘Stigmidium’ psorae group. To facilitate discussion of the distinguishing features of this group, a table comparing the terms referring to hamathecial hyphae in pyrenocarpous ascomycetes is presented.