Vegetative hyphae: hyaline Pseudothecia: black, globose, immersed to sessile, gregarious, (100-)125-150(-200) µm in diam. wall: upper part black to dark brown, c. 25 µm thick, lower part: medium to light brown, 10-20 µm thick, consisting of 3-5 cell layers hamathecium: indistinct or with few paraphysoids among the asci, branched and anastomosing, 1-3 µm thick; hymenial gel: often I+ violet asci: broadly cylindrical to broadly clavate, sessile or distinctly stipitate, 54-75(-80) x 19-25 µm, 8-spored, young asci with ocular chamber; endoascus: I- and KI-, BCr- ascospores: hyaline initially, becoming pale brown, 1-3(-5)-septate, constricted at the septa, upper cell slightly thicker than the lower one, mostly with 1 oil droplet per cell, ellipsoid, distichously arranged in the asci or not, (16-)17.5-22(-23.5) x (5-)5.5-7.5(-8) µm; walls: smooth, thin or with gelatinous sheath, BCr-, I-; epispore: partly BCr+ blue Pycnidia: 40-100 µm in diam.; with a dark brown wall conidia: hyaline, clavate, 3.5-5 x c. 1 µm. Hosts: upper side of thallus, or sometimes on the medulla of the lower side of squamules of Psora crenata, P. decipiens and P. saviczii; in Arizona on P. decipiens World distribution: Europe, Asia (Afghanistan), North America (U.S.A.) Sonoran distribution: once collected in south-central Arizona. Notes: Stigmidium psorae is one of three known taxa belonging of the so-called Stigmidium psorae group, characterized by a net of branched and anastomosing, rudimentary interascal filaments (for further information see Calatayud and Triebel ).