Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Life habit: lichenized Thallus: immersed, endoxylic or endophloedal, often staining the substrate gray, or episubstratic, thin, minutely granular, grayish green Apothecia: 0.8-1.3 mm high, 7-11 times as high as the width of the stalk stalk: 0.4-1.5(-4) x 0.05-0.12(-0.4) mm, 10-15 times as high as wide, dark red-brown to black, with colorless gelatinous mantle; central part: consisting of densely intertwined and irregularly arranged 2-3 µm thick hyphae capitulum: subglobose to lenticular, 0.18-0.4(-0.8) mm wide, with brown pruina (K+ purple-red crystals) on lower side of exciple and sometimes upper part of stalk exciple: dark brown, consisting of isodiametric to slightly elongated, heavily sclerotized cells; outer surface: covered by a smooth to strongly irregular layer of brownish, amorphous crystals; hypothecium: blackish brown with convex upper surface asci: when mature, cylindrical, 36-44 x 3.2-4.3 µm, with uniseriately arranged spores ascospores: mature spores: ellipsoid, (6.7-)8-11 x 4-5 µm, with regular ornamentation of spirally arranged ridges and occasional irregular cracks, particularly in old spores Pycnidia: spherical, semi-immersed, 0.06-0.12 mm in diam., producing different types of conidia on the same thallus; wall: 6-9 µm thick, dark brown, pale at the base, but close to the ostiole it has a very thick dark brown pigment layer covering the outer wall; conidiophores: Type V or VII of Vobis (1980), 1.5-2.5 µm thick, branched and anastomosing, with 3-6 µm long cells; conidiogenous cells: 2-3 x 1-1.5 µm conidia: acrogenous or pleurogenous, non-septate, hyaline, broadly ellipsoid to ellipsoid, 2-2.5 x 1.5 µm, often slightly curved or of irregular shape or very narrow and curved, vermiform, 5-8 x <1 µm Spot tests: thallus K+ dull yellow or yellow-red, C-, KC+ dull yellow turning orange P+ faintly yellow to orange, UV-; brown pruina: K(25%)+ violet-red, feather-like crystals; all parts of apothecia I- Secondary metabolites: thallus +placodiolic acid and +norstictic acid. Substrate and ecology: on dry, acid bark, especially on old willows or old oaks, in parks and open deciduous forests, and on wood (stumps, fenceposts), in moderately shaded situations in coniferous forests World distribution: northern boreal zone to subtropics in Europe, Asia; North, Central and South America, Australasia, and Africa Sonoran distribution: Arizona mostly moderate to high elevations. Notes: Calicium salicinum is characterized by the immersed or thin K+ yellow thallus, brown pruina on the lower side of its exciple, which forms a red precipitate with K, and its spores with spiral ornamentation.