On sandy mortar in coastal location.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
Nigel, I have photographs of expertly (BJC) named Collema tenax var. tenax from a BLS meeting and your material matches this very well, including the slightly crenulate apothecial margins. From other photographs from the same meeting I would say it is not var. vulgare, and I don't think the description of var. corallinum quite fits.
There is a problem in Smith in that it talks about three morphs when there are four mentioned - var. tenax is not explicitely described. Fortunately the Nordic Lichen Flora (vol. 3, Cyanolichens) has a much more clearly written summary (but six varieties) and from their key I would say definitely var. tenax.
(The Nordic Flora confirms the different spore size in C. bachmanianum and their photo, admittedly of a dried herbarium specimen, does not match your photos here.)
Honestly, I can't thank you enough Alan. Your input is always invaluable, and here, for me, it is treasurable, especially when backed by the legendary BJC!
Dobson doesn't mention the margins for C. tenax, but made me want to investigate the possibility of C. bachmanianum, hence my look at the spores. Smith et al. made me wonder about var. corallinum, and 'Lichens of Ireland' tells me "Discs are smooth, as are the rims, although they may become warted". Presumably smoothly-warted.
So thank you!
I note you have edited this. I kind of agreed with your first version ...
... enough said ;¬)
Lat/Lng: 52.972389, -4.46583
OS grid ref: SH345445