Apothecia: dark brown to black (K-), single or in small groups on thallus and apothecia of the host lichen, erumpent, sessile to substipitate, 0.1-0.15 mm in diam., round to irregular, often urceolate, with plane to slightly concave discs, with distinct to thick black, rough to striate margin exciple: externally dark brown (I+ brown to red-brown), internally hyaline, 20-35 µm thick, marginally cells arranged in radial rows, composed of +ellipsoid cells 3-5 µm in width hymenium: hyaline, 60-70 µm tall, hymenial gel I+ bluish brown to reddish brown, dark brown above forming an epihymenium 8-10 µm thick paraphyses: septate, branched and anastomosing, 1.5-2 µm wide; apical cells: with thick dark brown caps, 2.5-4.5 µm wide, caps elongate hypothecium: hyaline, 30-40 µm thick, pseudoparenchymatic asci: clavate, 58-64 x 13-16 µm, with external I+ blue amyloid cap, 32(-64)-spored ascospores: medium brown, 1-septate, ellipsoid, (4.5-)5-6.5(-7) x 2.5-3.5(-4) µm; wall: thin, smooth Conidiomata: not observed. Host: thallus and apothecia of Lecanora caesiorubella subsp. merrillii, commensalic World distribution: endemic to the Sonoran region Sonoran distribution: southern California, so far known only from Santa Cruz Isl. and Santa Rosa Islands. Notes: Among the Dactylospora species with polyspored asci, D. pleiosperma is characterized by its hyaline hypothecium, its spore size, its lack of a K-reaction of the epihymenial pigments, and its host selection.