Lecanora strobilina
A mainly lignum species, easily over looked as Lecanora symmicta, but separated by the distinctive non-corticate thalline margin and the lack of a K/UV (wet)+ bright green-yellow fluorescence, indicating a lack of xanthones. Found increasingly in good quality lignum habitats, mainly natural but also old worked lignum.
Thallus continuous or dispersed, granular to irregularly subareolate, ± undelimited, uneven, white to white-yellow or pale yellow-green, surface not corticate and developing a pruinose coating of projecting crystals to 0.1 mm in length in dried specimens; prothallus inconspicuous. Apothecia to 1 mm diam., aggregated, sessile, the base slightly constricted; thalline margin entire to crenulate, finally excluded, not corticate, whitish-grey or sometimes concolorous with the thallus; disc flat to somewhat convex, grey-yellow to pale red-, orange- or grey-brown; epithecium colourless, often interspersed with colourless granular crystals; hymenium 35–55 µm tall; hypothecium with small granular crystals; paraphyses 1–1.5 µm diam., unbranched or sparsely branched, the apices not swollen. Asci 35–45 × 10–17 µm. Ascospores 10–13 (–16) × (3–) 3.5–4 (–5) µm, narrowly ellipsoidal and often somewhat reniform. Conidia ca 25 × 1 µm, curved. Thallus C–, K+ yellow to brown, KC± yellow, Pd–, UV+ pale orange [spot tests on European material are reported as all negative]; (usnic acid, ± zeorin, ± decarboxysquamatic acid).
A member of the L. symmicta group and thus a candidate for segregation into the genus Zeora Fr. (Ivanovich et al., in prep.). Most likely to be mistaken for C– chemotypes of L. symmicta which are separable by the corticate thallus and exciple that becomes excluded, the less strongly yellow colour (usnic acid absent), and the K/UV (wet)+ bright green-yellow fluorescence. Old dried specimens have a distinctive whitish, waxy appearance. Has a similar chemistry to L. compallens, but this is sorediate and is sterile.
On hard dry lignum of Oak and Sweet Chestnut, also on bark, mainly of conifers and on worked timber; rare, but either under-recorded or recovering from past declines due to pollution.

Channel Islands, Isles of Scilly, southern England, N. Wales, Lake District, S.W. Ireland.
This species seriously declined in the 19th and early 20th century (Laundon, 1976) and had few records afterwards and was assessed as VU D2 in 2012 (recorded from a small Area of Occupation (AOO) and potentially likely to be come Critically Endangered or Regionally Extinct). Since then it has been found increasingly in good quality lignum habitats in Wales and south west and west England. Some of these sites are very lichen rich ones but others were rather ordinary locations. This is suggestive of a relatively mobile species recovering from past acidifying pollution, but associated with high quality habitat. It now exceeds the AOO limits for VU D2 and appears to be increasing, so may now be better assessed as Notable.
Britain: Vulnerable (probably no longer valid)
Wales: Vulnerable
Cannon, P., Malíček, J., Ivanovich, C., Printzen, C., Aptroot, A., Coppins, B., Sanderson, N., Simkin, J. & Yahr, R. (2022). Lecanorales: Lecanoraceae, including the genera Ameliella, Bryonora, Carbonea, Claurouxia, Clauzadeana, Glaucomaria, Japewia, Japewiella, Lecanora, Lecidella, Miriquidica, Myriolecis, Palicella, Protoparmeliopsis, Pyrrhospora and Traponora. Revisions of British and Irish Lichens 25: 1-83.
Laundon, J, R., (1976) Lichens New to the British Flora 5. The Lichenologist 8: 139-150
Text by Neil A Sanderson based on Cannon et al (2022)