Lecanora hybocarpa? in Newtonmore vc96 Scotland
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Coincidentally to the recent Norwich post, I’ve been looking at a birch bark lichen from Sue Thomas in Newtonmore, Scotland (I was hoping it might be a ‘proper’ Lecanora chlarotera to compare with what I think are probably L hybocarpa locally in Warwickshire). These appear to be L hybocarpa, with large marginal crystals that don’t dissolve in K, and epithecial crystals that penetrate down between the paraphyses (and which do dissolve in K). K+y. C-. Margins are Pd-. UV fluorescence is somewhat orange-brown, but not very bright, and easy to discount.
There seems to be a distinct fimbriate prothallus though, which has also confused me on the Warwickshire twigs, as both L hybocarpa and L chlarotera say no prothallus in LGBI and Dobson. Am I misinterpreting it?
[attachment=1]DBBC581C-707C-4786-9C7A-014427984C38.jpeg[/attachment] Thanks to Twitter discussion about using polarising filters, I can now take photos via the trinocular camera (one filter balanced on a Petri dish over the light source, the other propped over the slide).
I tried cutting some sections with the apothecium upside down, and the granule distribution was much the same. (I’d previously thought maybe the granules were just smeared down by the sectioning.)
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[attachment=0]D2A66C43-B168-4B32-9B07-AED37669B286.jpeg[/attachment] The literature has been inconsistent in the way the term prothallus is used. Some authors have used the term to mean a marginal zone composed only of fungal hyphae. Other authors have also used the term prothallus when referring to a pigmented boundary zone between separate lichen thalli. I produced an expanded and revised draft definition for LGBI3: 
[attachment=0]EMkeIp4WkAEPoU8.jpeg[/attachment] As for the presence of true prothalli in the
L. subfuscagroup, I note that the descriptions for L. chlaroteraand L. hybocarpahave been slightly revised in LGBI3 and so, for example, in L. hybocarpa: “prothallus white, sometimes conspicuous when the thalli are expanding rapidly.” I agree with this amendment as a white prothallus is sometimes visible, especially when young thalli are isolated and growing on hard, smooth bark. https://britishlichensociety.org.uk/sites/default/files/Lecanoraceae.pdf L. hybocarpaalso often has dark boundary lines where thalli abut other lichen thalli, including of the same species. I consider that you were correctly interpreting the presence of a prothallus when observing a white fimbriate margin. I too am still awaiting my first examination of true
L. chlarotera; I don’t seem to have a single specimen of it in my herbarium. Just to encorage people photos; of Lecanora chlarotera: 
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A dark disk morph ofLecanora chlaroteraon Oak twig in Mark Ash Wood, New Forest 
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Cross section of apothecia of above in polarised light. The very sharp line at the base of the crystals is characteristic.I am find this most on twigs in clear air areas and it is often the only twig species of
Lecanorain north Welsh rainforests. Dashing around Bramshaw Wood trying to get Lecanora hybocarpafor sequencing in February I got several Lecanora chlaroteraspecimens from low shaded twigs and no Lecanora hybocarpa. So clean air areas and less sunny twigs may be good places to look for Lecanora chlarotera. Neil
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