Caloplaca badioreagens is a new endolithic species of subgenus Pyrenodesmia characterized by a greyish brown, K+ reddish brown epithecium, and simple, non-capitate paraphyses. It is readily distinguishable from other endolithic Pyrenodesmias (C. agardhiana, C. alociza, C. erodens) by the presence of an unknown lichen substance in the excipulum and the subhymenium, forming large, rectangular crystal plates in GAW and GE. The new species was collected on hard limestone in three localities of central and southern Italy.