A disease of penstemon (Penstemon digitalis) occurring in commercial nurseries in Minnesota in 2004 to 2006 and characterized by red foliar ringspots, leaf deformation, and plant stunting was found to be caused by a strain of Turnip vein-clearing virus (TVCV) that was named Penstemon ringspot virus (PenRSV). This is the first report of a viral disease of penstemon. The genome organization of PenRSV was similar to that of the crucifer-infecting tobamoviruses. The nucleotide sequence of PenRSV was almost identical (99%) to that of TVCV, but the two viruses differed importantly in host range and symptoms induced. The only sequence difference between PenRSV and TVCV occurred at the 3′ end of open reading frame I, where the amino acid sequence FRDSNL in TVCV is replaced by FRGQQL in PenRSV. The experimental host range of PenRSV included species in the families Brassicaceae (Cruciferae), Cactaceae, Cucurbitaceae, Leguminosae, Malvaceae, and Solanaceae. This virus poses a potential threat to commercial nursery and bedding plant production because of its wide host range and because it will escape detection by immunoenzymatic screening procedures for tobamoviruses based on use of antibodies to Tobacco mosaic virus (TMV).