Thallus: areolate to rimose, sometimes with radiating fissures (especially when growing on bark or wood), 2-12(-15) cm in diam., 0.1-0.4(-2.0) mm thick areoles: angular to rounded or irregular, sometimes extenuated and radiating, flat to slightly convex or uneven, (0.3-)0.5-1.2(-2.3) mm in diam., contiguous prothallus: usually well developed (but sometimes missing in saxicolous specimens), at the thallus edge, zonal or fimbriate, dark blue-green to black with a ±bluish or greenish tinge, often with a white outer margin, (0.2-)0.4-2.5(-4) mm wide surface: gray with a ±bluish tinge, sometimes green-gray, olive-gray or brown-gray, rarely partly brown, dull upper cortex: (10-)15-35(-45) µm thick, uppermost part brown to green-brown, 5-15(-20) µm thick, with cells (4-)5-7(-9) µm in diam.; cortex covered with an epinecral layer (0-)2-10(-15) µm thick photobiont: chlorococcoid, cells ±round, 5-17(-22) µm in diam Apothecia: aspicilioid, rather common, (0.1-)0.2-0.6(-1.3) mm in diam., 1-2(-7) per areole, usually round, sometimes angular or elongated disc: black to blue-black, concave to flat, lacking pruina thalline margin: flat to slightly elevated, concolorous with thallus, rarely darker or with a thin, white rim exciple: (15-)20-60(-100) µm wide, I- or rarely minor parts I+ blue; uppermost cells brown to green-brown, ±globose, 4-6(-7) µm in diam. epihymenium: blue-green to green, rarely olive, without or with a few crystals, N+ intensifying blue-green, K+ green-brown to brown hymenium: hyaline, I+ persistently blue or partly turning yellow-green, (100-)130-160-200(-250) µm tall paraphyses: moniliform, rarely submoniliform, with (1-)3-5(-8) upper cells ±globose, (2.5-)3-5 µm wide, in lower part 1.5-2(-2.5) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I ±blue, persistent or partly turning yellow-green, overall 30-80(-100) µm thick asci: clavate, (60-)70-120(-140) x 20-31(-35) µm, 8-spored ascospores: hyaline, simple, ellipsoid, (16-)18-25(-31) x (8-)10-15(-17) µm Pycnidia: immersed, rather often present, 1-2(-5) per areole, 120-200 µm in diam., with a black, punctiform or somewhat elongated ostiole 50-100(-120) µm in diam. conidia: filiform, straight or slightly curved, (12-)16-27(-35) x 0.6-1(-1.5) µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: none detected by TLC. Substrate and ecology: on siliceous rocks, or on bark, including Calocedrus decurrens and Abies concolor, and lignicolous on Sequoia, usually in shaded and sometimes moist habitat, in forests, gorges with riparian vegetation etc. World and Sonoran distribution: apparently endemic to California, where it is found in Los Angeles, Riverside, San Diego, Santa Barbara and Tulare Counties, at 525-2230 m. Notes: Aspicilia cyanescens is characterized by its areolate to rimose thallus, sometimes with radiating fissures (especially well developed on bark or wood), a gray surface with a ±bluish tinge, a conspicuous dark blue-green to blue-black prothallus at the thallus edge (sometimes not so well developed in specimens on rocks), its ±blue-green epihymenium, its large spores and its long, filiform conidia. Specimens from Tulare County (Sequoia National Park) are usually lighter gray and somewhat thicker than specimens from the more southern counties in California. DNA (ITS) has been analyzed in three specimens (all from Riverside County): the type specimen on bark (Knudsen 2858) and two saxicolous specimens (Owe-Larsson 9151 & 9156). Phylogenetic analysis incorporating these and other specimens of Aspicilia confirm the uniqueness of the new species. Aspicilia confusa differs from A. cyanescens by its convex, ±dispersed areoles with gray to gray-brown color and its green to olive or olive-brown epithecium. The two species agree in several microscopical characters and some atypical specimens could therefore be difficult to determine. Aspicilia fumosa differs by its lighter gray thallus, its large apothecia with a darker thalline margin, its epihymenial color and somewhat shorter conidia than A. cyansecens; A. americana, common in Arizona, differs by its brown to gray thallus color in a mottled pattern, by usually having an indistinct prothallus and its epihymenial color; Aspicilia aff tenuis, differs by its ±brown thallus, its thalline margin with a white rim, its epihymenial color and submoniliform paraphyses. Aspicilia cyanescens is the only Californian Aspicilia-species growing on bark or wood. Megaspora verrucosa var. mutabilis, which also grows on bark and is common in the mountains of Arizona, differs in its apothecial appearance and by having larger spores (over 30 µm long). Kerry Knudsen, who collected the holotype, also reports A. cyanescens from two other localities in California (San Jacinto Mountains and Mount Palomar), where it grows on bark of Calocedrus decurrens. Some specimens (collected by Blakeman; MIN) from Sequoia National Park, Tulare Co., show some resemblance to A. cyanescens, but differs by the rather convex, partly brown and somewhat shiny areoles, and by the epihymenium which is usually green to olive, but sometimes blue-green. These specimens need further study.