Lichen? for ID please

[Teal]

Not a bril photo but this was growing on an upland stone wall. My guess is Xanthoria species

[JennyS]

No its not a Xanthoria as they are foliose (with leaf-like lobes) and this lichen is crustose.
Opegrapha gyrocarpa is a possibility if it was an acidic stone wall.

[Teal]

Thanks for that Jenny. Have done a bit more digging and wondered if it might in fact be Belonia nidarosiensis. The photo on the British Lichens site looks very much like my pic. However, as you will have guesed, I know absolutely nothing about lichens so am prepared to accept you diagnosis.

[JennyS]

Do you know what sort of stone the wall was made from?

Belonia nidarosiensis occurs on sheltered, shaded limestone, mortar etc whereas Opegrapha gyrocarpa is found on shaded acidic rocks.

The difficulty when trying to identify lichens from photographs alone is that there are many similar-looking ones so checking their habitat gives additional ID pointers.

The LichenIreland website is useful for checking details of possible visual identifications:
http://www.habitas.org.uk/lichenireland/splist.asp

[AlanS]

I agree with Jenny that this is Opegrapha gyrocarpa.

It can indeed be difficult to separate from Belonia nidarosiensis, but often has a smoother appearance and, as Jenny has said, is characteristic of 'acidic' stonework. (I know a geological lichenologist who gets very upset when rocks are described as "acidic", and he is correct, but I'll stick with the term.) Upland stone walls are a common habitat.

Both species vary in colour and without habitat or chemical data, identification from photographs is not easy. In this case I think the clincher is that the photograph shows the orange patches to be bounded by dark lines. This is the black prothallus that O. gyrocarpa has, and which Belonia does not!

Also, the yellow-green lichen shown out of focus to the right, in the shelterered crevices between the stones, looks very like Psilolechia lucida, another acidophilic species and a common associate of Opegrapha gyrocarpa.

To compare the two species further:
Belonia nidarosiensis (images of British lichens)
Opegrapha gyrocarpa (images of British lichens)

Alan
(who apologises for recent absence, too busy plus forum pages not loading properly for me)