Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
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Hymenelia epulotica is a rather rare lichen forming extensive, smooth, deep cream crusts on limestone rocks.
This, whatever it is, has a crust that is cracked into white 'areoles', which apparently have something more orange on top, but the definition of the photographs is, I regret to say, not good.
We need better photographs I am afraid, but rule out H. epulotica.
Yes, my camera isn't the best, I'm aware of that.
Lichen identification is extremely hard I've found, and not having a good book on them doesn't help matters.
What else might it be?
What annoys me about these photographs is that I really cannot think of any ideas. It is probably something very common and obvious, but I really have no idea.
And even with very good photographic equipment, getting decent photographs of these crusts on walls is amazingly difficult. So much depends on minute details of surface features that the slightest camera movement or insufficient depth of focus is enough to lose all definition. I use various tripods for different situations and still discard a high proportion of my photographs.
Lat/Lng: 51.5932, -2.9694
OS grid ref: ST329887