Life habit: lichenicolous, parasymbiotic, non-lichenized Ascomata: usually in dense clusters of 0.5-4 mm in diam., at first immersed, punctiform, later almost superficial, rounded or often oblong-ellipsoid, black, epruinose, 0.15-0.7 x 0.1-0.2 mm; disc: first slit-like, becoming widely exposed, black, epruinose exciple: closed, thick, dark brown hymenium: hyaline, I+ blue quickly turning red; hypothecium pale brown, up to 45 µm high; epihymenium: brown; paraphysoids branched, 2 µm thick asci: cylindric-clavate to clavate, without an apical K/I+ blue ring, c. 45-55 x 16-18 µm, 8-spored ascospores: (12-)14-17 x (4-)5-6.5 um, oblong-ovoid, hyaline, 3-septate, not or slightly constricted at the septa (Parasitica-type); perispore: 1 µm, hyaline, becoming dark brown granulose when over-mature. Pycnidia: immersed, in close proximity to ascomata, black conidia: cylindrical, straight, simple, 6-7.5 x 1 µm. Substrate and ecology: on thalli of species of the Xanthoria parietina group World distribution: Europe, Africa (Marocco, Canary Islands), Asia (Israel) and North America Sonoran distribution: Mexico (Baja California and Baja California Sur). Notes: Opegrapha physciaria is characterized by its ascospores, asci without an apical K/I+ blue ring and occurrence on thalli of species of the Xanthoria parietina group. The record from California on Caloplaca rosei (Cole and Hawksworth 2001) is very doubtful as an examination of the corresponding specimen did not allow to find ascomata of O. physciaria, but only ascomata of Stigmidium cerinae and some from a lichenicolous fungus with apothecioid ascomata and 1-septate ascospores (cf. Buelliella inops).