Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: areolate, rarely rimose at edge, 3-7 cm in diam., (0.1-)0.2-0.5(-1.5) mm thick areoles: angular, sometimes irregular or elongated, flat to sometimes concave or uneven, rarely convex, (0.2-)0.5-1.4(-2.7) mm in diam., contiguous, separated by small to rather large cracks, rarely dispersed prothallus: indistinct or thin, at the thallus edge, black to blue-green, rarely with a white outer margin, sometimes fimbriate, 0.1-0.3(-0.6) mm wide surface: medium to dark brown, yellow-brown or olive-brown to olive, sometimes with white or pale edges of the areoles, dull to ±shiny upper cortex: cortex 20-30(-40) µm thick, uppermost part brown, 5-10(-15) µm thick, with cells (4-)5-7 µm in diam.; cortex covered with an epinecral layer 5-15(-20) µm thick photobiont: chlorococcoid, cells ±round, 5-20 µm in diam. Apothecia: aspicilioid, common to rather common, (0.1-)0.2-1.0(-1.3) mm in diam., 1-2(-7) per areole, round to angular, sometimes linear or irregular disc: black, concave to plane, rarely convex, without pruina or sometimes with a thin white pruina thalline margin: thin, flat to ±raised, rarely prominent, often forming a white or light gray rim around the disc, or concolorous with thallus exciple: (15-)25-50 µm wide, I-, rarely I+ blue medially, uppermost cells brown, ±globose, (4-)5-6(-7) µm in diam. epihymenium: green to olive, olive-brown or brown, without or with a few crystals, rarely with numerous crystals, N+ blue-green to green, K+ brown hymenium: hyaline, I+ persistently blue or partly blue-green to yellow-green, (110-)140-200(-230) µm tall paraphyses: submoniliform to slightly moniliform, rarely non-moniliform (upper cells cylindrical, not or slightly constricted at septa), with (0-)1-5(-7) upper cells ±globose to subglobose or subcylindrical, uppermost cells 3-5 µm wide, in lower part (1.2-)1.5-2(-3) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue, together 40-60(-80) µm thick asci: clavate to sometimes ovoid, (80-)90-140 x 20-30 µm, 8-spored ascospores: hyaline, simple, ellipsoid, (18-)20-27(-31) x (10-)12-17(-18) µm Pycnidia: rather common, 1-3(-12) per areole, immersed, sometimes with a white rim, rather often aggregated in linear or ±branched formations (then up to 600 µm in diam.), 120-220 µm in diam., with a black, punctiform to sometimes elongated ostiole, 50-100(-120) µm in diam conidia: filiform, straight or slightly curved, 5-12(-22) x 0.8-1 µm Spot tests: medulla I-; cortex and medulla K+ red to yellow, P+ orange, C- Secondary metabolites: stictic acid and trace norstictic acid (including type specimen), rarely with hyposalazinic acid instead of norstictic acid (1 specimen, Owe-Larsson 9148) or with norstictic acid alone (1 specimen, Owe-Larsson 9119). Substrate and ecology: on exposed to shaded siliceous rock World and Sonoran distribution: Riverside Co. (San Jacinto Mountains) and Los Angeles Co. (Santa Monica Mountains) in southern California, at 890-1680 m Notes: Aspicilia knudsenii is characterized by its usually brown to sometimes olive-brown or olive thallus with rather large apothecia, its large ascospores, its usually short conidia and the presence of stictic acid as a major substance and norstictic acid usually as a minor substance. The combination of these characters clearly separates it from other Aspicilia species. DNA (ITS) has been analyzed in four specimens, including the type (Owe-Larsson 8472, 9119, 9145 & 9148). The two specimens from Los Padres National Forest, Kern Co., differs by sometimes having long conidia (8-22 µm), but in other respects agree well with A. knudsenii. Aspicilia anglica differs by having longer conidia and containing substictic acid; Aspicilia cuprea differs by having a different shade of brown thallus color and its longer conidia, Aspicilia olivaceobrunnea differs with respect of the thallus color and its usually longer conidia; Aspicilia pacifica and Aspicilia santamonicae differ by having thinner thallus and smaller apothecia, and A. santamonicae contains only norstictic acid.