Churchyard lichens - id help please

[chrisjohnson]

The following were photographed on grave stones in a coastal cemetery in North Uist.
We have tentative identification of Aspicilia caesiocinerea and Caloplaca crenularia. Comments would be appreciated.
Thank you

Chris

[AlanS]

Hi Chris,

The Caloplaca crenularia is correct, and from your other post I assume you know you have Ochrolechia parella in each of these photographs (a very common species on the Uists).

The upper photographs, however, are not Aspicilia caesiocinerea. This has the apothecia initially sunk into the thallus surface and they are rather small and irregular in shape. Here we have conspicuous, black-disked apothecia that are "superficial" from the start.

The lichen is either Tephromela atra or Lecanora gangaleoides, both of which are common, especially on base-poor rocks and especially near the coast (and they can grow together, looking near identical). As your photographs show the thallus surface to be rather smooth between the cracks, my guess would be Tephromela atra, but I cannot be 100% positive from a photograph.

The best field way to distinguish them is to pick at the thallus surface with a fingernail. Do this with L. gangaleoides and you expose distinct yellow-orange tissue (anthraquinone pigment) in the lower layers of the thallus (easily visible with a lens). The tissue of Tephromela remains grey-white within. The good thing about churchyards is that one can usually find the same photographed lichen again to check things like this.

Alan

[chrisjohnson]

Thank you.
We will make a return visit at some time during the next few months and confirm the id.

Chris