Thallus: to ca 10 mm diam., mostly immersed in the substratum, the surface white to pale silver grey, sometimes slightly farinose.
Anamorph: not known.
Teleomorph: ascomata apothecia, 200-600 (-800) µm diam., scattered to somewhat crowded, sessile, disc flat to slightly concave, red-brown, sometimes faintly granular but not pruinose. Margin concolorous to slightly paler than the disc, initially prominent but usually eventually becoming excluded, rarely flexuous. Excipulum 25-50 μm wide, with few or no algal cells; the inner part narrow and poorly developed, composed of interwoven hyphae in a gelatinous matrix, the outer part pale brownish. Hypothecium hyaline, containing oil droplets. Subhymenium hyaline. Hymenium to 60 μm high, hyaline or with a diffuse reddish to brownish coloration in the upperpart. Interascal tissue of branched and sometimes gelatinized paraphyses, terminal cells simple or swollen, 2-5.5 μm diam., hyaline or eventually conglutinated and coloured reddish brown. Epithecium K+ purple. Asci 50-55 × 15 μm, clavate, usually 8-spored. Ascospores 9.5-13 × 5-5.5 μm, ellipsoidal, 1-septate, the septum median and 3-4.5 μm thick, hyaline, smooth, without a gelatinous sheath or appendages.
Chemistry: thallus K–, apothecia K+ purple.
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Assessed as Vulnerable (D2) by Woods & Coppins (2012). Reported from three sites in northern Scotland, two on Shetland (Mainland) and a recently discovered site on the island of St Kilda. The two Shetland sites were on old but unrotted fence posts, and therefore vulnerable to destruction as fences are replaced. Both sites were resurveyed in 2015. The species was not rediscovered, and as most of the fence posts appeared to be quite new, it's likely that these populations no longer exist. The St Kilda population was overgrowing rotten vegetation. It's possible that this represents a more typical habitat for the species; northern Arctic populations are reported on wood, detritus and even reindeer droppings. It should be sought in similar habitats in the extreme north of Scotland.
Superficially more similar to a species of Lecanora or Lecania, but the K+ purple epethicium and ascospores with thickened septa are typical of Caloplaca. The red-brown colour of the discs and the margin that becomes excluded are distinctive features when compared with other Caloplaca species on bare wood or plant detritus.
In GB&I, reported from wood of old but unrotten fenceposts, and on plant detritus on the ground.
Three localities are known, two in VC112 Shetland and one in VC110 Outer Hebrides (St Kilda).