Thallus: areolate, (1-)2-10(-15) cm in diam., (0.1-)0.2-0.6(-1.5) mm thick areoles: rounded to verrucose, sometimes angular or irregular, ±convex, rarely flat, (0.2-)0.4-1(-2) mm in diam., usually ±dispersed, sometimes contiguous and separated by ±large cracks prothallus: often present, at least in parts along the thallus edge, mostly fimbriate, black to brown-black, sometimes blue-green in outermost part, (0.2-)0.5-2 mm wide surface: gray to brown-gray or gray-brown, rarely brown, beige, white-gray or blue-gray, sometimes in part of the areoles with a thin, white pruina; dull to sometimes slightly shiny upper cortex: (12-)20-35(-40) µm thick, uppermost part ±brown, 5-10(-20) µm thick, with cells 5-7(-9) µm in diam.; cortex covered with an epinecral layer (0-)2-10(-12) µm thick photobiont: chlorococcoid, cells ±round, 5-17(-22) µm in diam. Apothecia: aspicilioid, usually rather common, (0.1-)0.2-0.8(-1.5) mm in diam., 1(-4) per areole, round, sometimes angular or elongated; fertile areoles often elevated disc: black, usually concave, sometimes plane, rarely convex, without pruina or rarely with a thin ±white pruina thalline margin: flat to ±elevated in older apothecia, sometimes prominent, concolorous with thallus or sometimes with a thin, white rim exciple: (20-)30-70(-80) µm wide, I- or sometimes partly I+ blue medially, rarely fully I+ blue; uppermost cells brown to olive-brown, ±globose, (4-)5-6(-8) µm in diam. epihymenium: green to olive or olive-brown, rarely brown, without or with a few crystals, N+ green to blue-green, K+ brown to green-brown hymenium: hyaline, I+ persistently blue or sometimes partly turning yellow-green, (120-)140-200(-230) µm tall paraphyses: moniliform, sometimes submoniliform, with (1-)3-5(-8) upper cells ±globose, 3-4.5(-5.5) µm wide, in lower part 1.5-2(-2.5) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue or sometimes partly turning yellow-green or partly I-, together (20-)40-80(-120) µm thick asci: clavate, (70-)80-120(-130) x (17-)20-30(-38) µm, 8-spored ascospores: hyaline, simple, ellipsoid, (15-)19-27(-30) x (9-)11-16(-20) µm Pycnidia: rare to rather common, 1-2(-4) per areole, immersed, sometimes with a white rim, rarely aggregated, (90-)120-200(-220) µm in diam., with a black, punctiform to rarely elongated ostiole, (40-)50-100(-110) µm in diam. conidia: filiform, straight or slightly curved, (11-)16-25(-28) x (0.6-)0.8-1(-1.2) µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: none detected by TLC. Substrate and ecology: on exposed to shaded siliceous rock, in open heath, chaparral, or in forest, often montane World and Sonoran distribution: southern and central parts of California, at (250-)550-3170 m. Notes: Aspicilia confusa is a rather variable species, characterized by a gray to gray-brown thallus with ±convex and ±dispersed areoles, a dark, fimbriate hypothallus, and round apothecia, usually one per areole. Furthermore, it has a tall hymenium, large spores, long conidia, and it lacks secondary substances. It is one of the more common Aspicilia species in southern and central California, especially in montane areas. Aspicilia confusa has hitherto been confused with European species like A. caesiocinerea or Aspicilia gibbosa. DNA (ITS) data from three specimens (Owe-Larsson 9087, 9093 and 9094, all from Riverside Co.), indicate that A. confusa is related to Aspicilia glaucopsina and Aspicilia phaea, but the variability of A. confusa needs further study. Aspicilia cyanescens differs from A. confusa by its blue-gray thallus, the flat, contiguous areoles, and the blue-green epihymenium. Spore and conidium size agrees with A. confusa, and some atypical specimens could therefore be difficult to determine. Aspicilia fumosa has a lighter gray thallus, scattered, large apothecia with a darker thalline margin, and somewhat shorter conidia than A. confusa. Aspicilia aquatica grows in moist habitat by streams and lakes, and has a contiguous areolate to rimose thallus with a different color, and submoniliform paraphyses. Aspicilia glaucopsina grows on soil and disintegrated granite and has a contiguous thallus. Aspicilia phaea has a brown to gray-brown thallus and shorter conidia than A. confusa. Some specimens from central and northern California (in ASU) with flat and contiguous areoles microscopically agree with A. confusa, and probably belong to this species, but need further study.