Lecanora caledonica
An attractive Lecanora, similar to Lecanora intumescens, and shares its characteristic white decorticate margins, but the disks are typically medium brown to paler beige and never pruinose and the thalline margin is Pd–. Only known from northern oceanic woodlands, north of the Great Glen.
Thallus continuous, smooth to finely cracked or areolate; areolae 0.3–1.3 mm diam., irregular in outline, of different shades of pale grey, sometimes yellowish grey; margin clearly delimited, sometimes by a thin black line against other thalli or as a white, slightly fimbriate prothallus. Apothecia normally present and abundant, 0.4–1.5(–2.0) mm diam., adnate to sessile, round to irregular to often angular from compression in dense aggregates; thalline margin prominent and persistent, (30–)50–150(–240) μm thick, level with or slightly raised above disc, even to uneven or somewhat ridged, of thallus colour or paler, without a differentiated cortex, with small crystals; disc varying greatly in colour from pale beige-orange to dark brown or almost black, normally matt, without pruina, slightly concave to somewhat convex, sometimes flexuous; beige-grey to brown-blackish, with small, POL+ granules on top and between the paraphyses ( pulicaris-type), dissolving in K but not in N, when dark pigment is present N+ red, K+ olive; paraphyses 1.5–2 μm wide, simple to slightly branched, straight to flexuous, with tips to 3 μm wide; hypothecium hyaline, 125–400 μm thick. Asci 50–68 × 11–17 μm, with eight spores; ascospores simple, narrowly to broadly ellipsoid or ovoid, ends round or slightly pointed, (9.0–) 10.0–13.0(–14.0) × (4.8–)5.0–8.0(–9.5) μm. Thallus and apothecial margin K+ yellow, C−, KC+ yellow, Pd+ pale yellow, UV− (atranorin, zeorin and an unknown substance that turns UV+ ice blue before charring and an additional substance in minor concentration).
Similar to Lecanora intumescens, but this has redder disks that are pruinose when young and has a Pd+ deep yellow thalline margin.
In northern oceanic woodland, on deciduous trees with smooth bark, most often found on the trunks, but also on coarse branches. Often on Alder, but more rarely on Sycamore, Hawthorn, Ash, Bird Cherry and Wych Elm.
In the Highlands north of the Great Glen. Otherwise only known from coastal regions of Norway.
Not assessed.
Arup, U., Holien, H. and Coppins, B. J. (2023) Lecanora caledonica – a new species in the Lecanora intumescens group (Lecanoraceae) from north-western Europe. The Lichenologist 55 Link
Text by Neil A Sanderson based on Arup et al (2023)