The new species Peltigera phyllidiosa Goffinet & Miadlikowska from the Southern Appalachians, eastern U.S.A., is closely related to P. collina and P. neckeri. Like these species it has a glabrous upper cortex and black fingernail- or saddleshaped apothecial discs, but differs in its laminal phyllidia. Variation in nucleotide sequences of the Internal Transcribed Spacer (ITS) of the nrDNA repeat region correlates with the presence or absence of phyllidia, supporting the distinction of P. phyllidiosa from P. collina and P. neckeri.