A Lecanora?

You haven’t started with the easiest type of lichen by any means but since it is growing in your garden it is understandable and sensible that you will be curious to study it. I am almost certain that this is Lecanora albescens. The trouble is that this belongs to a group of lichens which are particularly difficult to study, the Lecanora dispersa group (recently transferred to the separate genus Myriolecis). In addition, I think there are more than one taxon which get lumped by lichenologists and recorded as L. albescens.

[attachment=0]Screenshot 2021-02-03 at 5.16.30 PM.png[/attachment]

I first started to seriously suspect that at least two taxa were involved when I studied them on the long, even concrete walls of Grafham Water near Huntingdon. However, in most situations it is much more difficult to distinguish them and there may be more than two taxa for all I know. If my Types A and Types B mean anything at all, I would suggest that you have Type B with very little thallus, brown discs (when dry) and thalline margins not or little raised above the discs.

https://twitter.com/obfuscans3/status/1062756711876964352

In your first micrograph you note the presence of brown-walled hyphae. These belong to a lichenicolous fungus, presumably a dematiaceous hyphomycete and this sort of thing often turns out to be Intralichen christiansenii. However, I tend to be wary of naming such things and can’t identify yours, just giving a suggestion of the sort of thing it is likely to be.

http://www.dorsetnature.co.uk/pages-lichen/lch-454.html

I’m afraid that the other micrographs don’t provide much information to help. This is not your fault, it is just that this group of lichens have few easy characters and often critical work involves noting the solubility of granules in various mountants. I would record this as Lecanora albescens and move on to something a bit easier!

You mention L. intricata, L. polytropa and L. symmicta. All of those contain usnic acid which gives the lichens a subtle dull yellowish green colour, something that you will get your eye in for once you have studied such species.

The new micrographs of the interior of the black dots do not belong to a dematiaceous hyphomycete! (I think the original micrograph now removed did show a fungus with brown walled vegetative hyphae). The one shown now is a different type of lichenicolous fungus with brown, septate (perhaps submuriform) ascospores in asci. This looks interesting. I don’t know its identity offhand but hopefully we can work it out. The only thing with similar spores that I have had in Lecanora dispersa agg. is Diplotomma parasiticum but that would have brown tipped paraphyses and brown hypothecium.

http://fungi.myspecies.info/taxonomy/term/7410/media