Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: areolate, 2.5-5 cm in diam., 0.3-0.7(-0.9) mm thick areoles: angular to irregular when larger, rarely round or with papillae, flat to convex, (0.2-)0.4-1.0(-1.5) mm in diam., contiguous, usually with small cracks prothallus: narrow, not always present, at the thallus edge, sometimes fimbriate, blue-black to black, rarely white in outermost part, 0.1-0.4 mm wide surface: medium to dark brown, rarely green-brown to gray-brown, often with white lines or spots, ±shiny upper cortex: 20-33(-40) µm thick, uppermost part brown, 5-12(-20) µm thick, with cells (4-)5-6(-7) µm in diam.; cortex covered with an epinecral layer 3-12(-25) µm thick photobiont: chlorococcoid, cells ±round, 5-16(-19) µm in diam. Apothecia: aspicilioid, rather common to rare, scattered, 0.2-0.6(-0.8) mm in diam., 1(-3) per areole, round to angular or often irregular, sometimes elongated disc: black, without pruina, concave thalline margin: at the beginning flat, ±elevated and prominent on larger apothecia, concolorous with thallus to light gray exciple: I-, rarely partly I+ blue, 30-50(-70) µm; uppermost cells brown, ±globose, 4-6(-8) µm in diam. epihymenium: green to olive or brown-olive, rarely brown, without or with few crystals, N+ blue-green to rarely green, K+ brown hymenium: hyaline, I+ persistently blue, (120-)140-160(-170) µm tall paraphyses: moniliform, rarely submoniliform, with (2-)3-5(-7) upper cells ±globose, uppermost cell (3.5-)4-5(-6) µm wide, in lower part (1.5-)2 µm wide, not or slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue, together (30-)40-60 µm thick asci: clavate, (60-)70-105 x 20-30(-37) µm, 8-spored ascospores: hyline, simple, ellipsoid, 18-26(-28) x 10-16(-18) µm Pycnidia: rare to common, 1-2(-5) per areole, immersed, sometimes with a white to gray rim, 150-200 µm in diam., sometimes aggregated in ±branched formations (up to 400 µm in diam.), with a black, punctiform to sometimes elongated ostiole, 70-100 µm in diam. conidia: filiform, 10-13(-14) x 0.8-1(-1.5) µm Spot tests: cortex and medulla I-, K+ red, P+ orange, C- Secondary metabolites: norstictic acid. Substrate and ecology: on exposed to shaded, siliceous rock at 790-940 m World and Sonoran distribution: Santa Monica Mountains in southern California. Notes: Aspicilia santamonicae is characterized by its medium to dark brown thallus, its scattered and often irregular apothecia lacking pruina and with an elevated and prominent thalline margin, its large spores, its rather short conidia, and the presence of norstictic acid. DNA studies of the type specimen show that A. santamonicae is related to but well separated from Aspicilia aurantiaca and Aspicilia pacifica. These species differ also morphologically from A. santamonicae. Aspicilia aurantiaca has an orange thallus and shorter conidia, while A. pacifica has a lighter thallus color (white to gray or brown), more numerous, regularly rounded to angular, pruinose apothecia, lacking a prominent thalline margin, and it contains stictic acid as a major secondary substance and norstictic acid usually only in minor amounts. Both these species are found at the type locality of A. santamonicae, and a specimen of A. pacifica from this locality has also been analyzed by DNA. Aspicilia anglica is separated from A. santamonicae by its longer conidia and the presence of substictic acid; A. cuprea differs by its thicker thallus, larger apothecia and long conidia; A. knudsenii differs by its thicker thallus, larger apothecia, submoniliform paraphyses and by usually having stictic acid as a major substance and norstictic acid usually only in minor amounts; A. olivaceobrunnea differs by the brown thallus color with an ±olive tinge, an apothecial thalline margin which is flat or only slightly elevated, and by the longer conidia. A specimen from Baja California Sur (Wetmore 79323; MIN) has a dark brown to almost black-brown color, and the apothecia have a discrete white pruina. In other respects it agrees well with the specimens from Santa Monica Mountains, and it might belong to A. santamonicae. This, however, needs further study.