Another crustose from last Sunday

[diatom dave]

This crustose lichen found on a sandstone wall has me completely stumped. I've included a piece of it magnified 10X. Can anyone help please?

[AlanS]

Hi Dave, see my remarks on your other crustose lichens, and that whatever names I produce are merely suggestions to be considered.

Here, the picture is puzzling, as there appear to be "excavate" soralia producing blueish soredia, but if so, then what are the greenish powdery patches? More escaped algae??

Well it seems most like Porpidia tuberculosa again, but I would not rule out P. soredizodes, even though the soredia seem dark for the latter. Chemical testing required!

Did you see my post in your "Tree Lichen?" thread, disagreeing with a previous suggested identification?

Alan

[diatom dave]

Hello Alan, I read your reply saying you thought it was R. fraxinea but I didn't reply until now because I wanted to check the specimen for myself to see if the colour was the same on both sides...and it was. Since first finding this one I have found a couple more and they are the same. Thanks for your reply.