White crustose lichen growing on mountain limestone. Almost spherical, orange apothecia. Possibly Protoblastenia calva.
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Some fungi are very poisonous so a mistaken ID could have serious consequences.
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I have similar photos on limestone that are P. calva (confirmed by the K+ red reaction in sections under the microscope).
Protoblastenia lilacina is very close to P. calva and has been confused for it. The former is described as sometimes having a lilac pigment in the hypothecium (tissue below the asci) and has apothecia that are K- or slightly darkening in K. I have yet to identify it, and don't know if the two species can be told apart in photos.
Thanks for help and information. (Previously seen only P. rupestris so encouraged even though this may be P. calva or P. lilacina.)
I agree with Nigel's comments. I have quite a few photographs of P.calva/lilacina now - still waiting to find time to do the microscope work so I can sort them out. I note that the appearance, especially apothecial colour, depend a lot on how dry the material is. As yet, I wouldn't try to name them from a photo.
Lat/Lng: 51.8529, -3.8409
OS grid ref: SN733187