Timdal, E. (1991). Monograph of the Genus Toninia (Lecideaceae, Ascomycetes). Opera Botanica 110: 37-39.

Differs from Toninia diffracta by smaller squamules, sometimes rosulate.  Species belonging to chemotype E (or rarely chemotype 0).

Thallus squamulose, indeterminate.  Squamules up to 2 mm diam., scattered to contiguous, more or less orbicular, often lobed to slightly rosulate, weakly to strongly convex.  Upper side pale grey, smooth to densely covered by more or less granular pruina, dull, often with shallow fissures in the cortex, lacking pores and pseudocyphellae.  Margin concolorous with upper side, pruinose.  Underside medium grey to dark brown.  Upper cortex 30-70 µm thick, lacking a distinct epinecral layer but densely encrusted (and partly overlaid) by crystals of calcium oxalate.  Algal layer continuous.  Medulla containing scattered crystals of calcium oxalate.  Lower cortex resembling upper cortex, but thinner and containing less or no crystals of calcium oxalate.  

Apothecia up to 1.5 mm diam., weakly concave to weakly convex, persistently marginate, epruinose to moderately pruinose.  Proper exciple medium brown to dark reddish brown throughout or with a darker grey rim, K- and N- or K+ violet and N+ violet (grey pigment), lacking or thinly overlaid by crystals of calcium oxalate.  Hypothecium medium brown to dark reddish brown in upper part, paler brown to almost colourless in lower part, lacking crystals.  Hymenium 60-70 µm high; epithecium grey, K+ violet, N+ violet, containing crystals of calcium oxalate.  Spores fusiform, 1-septate, 12.5-21.5 X 3-4 µm (n=28).  

Pycnidia not seen.

Chemistry: Chemotype 0 or E.

Variation.  The species is not very variable.  The shape of the squamules varies from orbicular to indistinctly rosulate.  Various amounts of pruina and fissures in the upper cortex give the upper side a surface ranging from smooth to granular.

Taxonomic Remarks.  The species closely resembles T. diffracta and T. subdiffracta.  Although most specimens of the three species are morphologically recognizable, some intermediate specimens do occur.  My choice of giving the three taxa rank of species is based on a combination of the vague morphological differences, chemical properties, and their geographical distributions.  Toninia arctica has smaller and more lobed squamules than (sic) two other species.  Specimens of T. arctica with well developed squamules become indistinctly rosulate, which is not seen in T. diffracta and T. subdiffracta.  The species has more convex squamules than T. subdiffracta, and more shallow fissures in the upper cortex than T. diffracta.  Toninia arctica belongs to the chemotype E (or rarely 0), T. subdiffracta to chemotype D (or rarely 0), and T. diffracta either to chemotype D, E, or 0.  The three species are allopatric; T. arctica occurs in arctic-alpine regions of Greenland and North America south to Alberta; T. subdiffracta in arid parts of western temperate U.S.A. (Arizona, Colorado, New Mexico, Utah), and T. diffracta in southern, central, and western Europe.

Acid deficient specimens of T. arctica may also be confused with the two sympatric species T. rosulata and T. sedifolia.  The former species differs in forming larger squamules and in having a more or less colour-less inner part of the exciple and hypothecium; the latter in forming larger, more irregular to bullate squamules, in the absence of fissures in the cortex, and in having farinose (not granular) pruina on the upper surface. 

Distribution and habitat.  The species is terricolous, and in many collections associated with cyanophilic lichens.  It is restricted to arctic-alpine areas of Greenland and North America south to Alberta. The recorded altitude ranged from about sea-level (Arctic) to 2350 m (Alberta).  The four acid deficient specimens examined were collected in Baffin Island (CANL), Banks Island (CANL), the Franklin Mountains (UAC), and the Sukakpak Mountains (S).