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Caloplaca scotoplaca (Nyl.) H. Magn.
Family: Teloschistaceae
Caloplaca scotoplaca image
Magnusson, AH. 1944. Stuides in the Ferruginea-group of the genus Caloplaca. Kongl. Gotheborgska Wetensk. Samhallets Handl., Wetensk. Afd. 60: p. 36-37

Thallus continuous, thin, grayish black, very minutely areolate, areolae 0.2-0.4 mm wide, 0.1-0.2 mm thick, irregular, plane to uneven, separated by very thin, often indistinct cracks, surface K+ dark green, black hypothallus more or less visible at the diffuse circumference.  Apothecia very dense, De 80-160 in central parts, appressed, 0.2-0.4 mm wide, disc plane or slightly convex, dark ferrugineous or ferrugineous brown, orbicular or angular, surrounded by a thin, regular, mostly persistent margin, concolorous with the disc, in young apothecia brighter, in older ones darker to extenuated.

Apothecia about 0.2 mm thick (with thallus 0.3 mm).  Gonidial stratum continuous, 35-50 µ thick below, sometimes developed also into the margin; cortex outside it 12-25 µ thick, cells 3-3.5 µ, globose, but +/- concealed by granules.  Exciple visible all round, refracting, 10-20 µ thick or at edge widened to 35 µ with 3.5-4.5 µ, rounded cells, exterior surface brownish yellow, I+ blue, or 10-15 µ I-.  Hypothecium 20-50 µ thick, grayish, its cells in KOH 2-4(5.5) µ, irregular, thin-walled, often lengthened, I+ dark blue.  Thecium 60-65 µ high, I+ dark blue, upper 11-15 µ dark sordid yellow, granular.  Paraphyses 1.7 µ, discrete in KOH, apices 4-5 µ, with 2-3 clavate cells, sometimes with single branches.  Asci 40-50 X 13-15 µ.  Spores 8, 10-12 X 7-7.5 µ, septum 4-5 µ (Descr. from MALME 443).

Conidia (in the authentic specimen) 2.5-3.5 X 0.7 µ, bacilliform, conglutinated.

Habitat.  On siliceous rock, presumably where there is more or less access to nitrates.

Distribtuion.  Common in southern Sweden, but no specimen seen N. of Uppland and Västmanland, but one specimen from the vicinity of Trondhjem.  From Central Europe a small number of specimens have been examined.

C. scotoplaca is characterized by the thin, dark, areolate thallus, the dense small apothecia with dark ferrugineous to +/- brown colour and distinct, but not prominent margin, the distinct, thin-walled cells in the exciple edge, the constrictedly septate, +/- globose apices of the paraphyses and the small spores with moderately thick septum.  It is usually found in the herbaria under the name of caesiorufa (also ferruginea v. obscura or festiva).

Variability.  The species is usually easily recognized and rather constant as to the thin, smooth, indistinctly areolate thallus.  But the thallus colour varies, probably mainly from factors due to the exposition, from quite black (f. obscura), grayish black (type) over +/- gray (f. cinerascens) to pale or yellowish (f. umbrosa).  When the thallus becomes exceedingly thin, the black hypothallus will be left (f. depauperata).  The usually dark apothecia may become almost black, their size and shape is fairly constant.

f. obscura (TH. Fr.) H. MAGN.  Thallus black.  Apothecia black-rusty or dark brown/grayish-brown black.

Is only a mean form, perhaps due to intense insolation.  Under C. ferruginea f. obscura TH. FRIES arranged mainly C. scotoplaca with its darkest forms but also C. festiva with +/- dark thallus.

f. cinerascens H. MAGN.—Thallus becoming ashy grey, thin or areolate-granular.  Apothecia brightly colored, sessile, distinctly marginate.

f. umbrosa H. MAGN.  Thallus pale, becoming yellow-ashy grey.  Apothecia brightly colored, rusty-orange.

Very obvious when intensely yellowish with pale apothecia but I have seen the colour of the crust pass from dark to light over the corner of a rock.  The structure of the apothecia is quite typical.

f. depauperata H. MAGN.—Thallus disappearing or formed from single hypothallus, apothecia dark.