A new lichenicolous discomycete, Cecidonia protoblasteniae, is described as new to science from the Russian Arctic. The new species is characterized by dark, superficial lecideine apothecia with a prominent margin; a cupular, dark brown exciple that is K−, N+ reddish brown; a greyish brown epihymenium; branched, anastomosing, coherent paraphyses that are apically hardly enlarged; 8-spored asci resembling the Porpidia-type; hyaline, broadly ellipsoid to subglobose, aseptate ascospores; and by its growing on Protoblastenia terricola. Key words: lichen parasites, Siberia, taxonomy.