There are several species that have this look and they have bounced around among genera. Since you have simple spores, I' suggest the Group 1 key of Lecidea in the Microlichens book, p. 344. It's not a true Lecidea, rather more of a historical Lecidea, but for convenience these are keyed together under Lecidea.
Most likely are Bryobilimbia hypnroum or Mycobilimbia berengeriana.