A flexuous virus was detected in a Cnidium officinale plant in Japan showing mosaic symptoms. The virus was assigned to the genus Potexvirus based on analysis of its complete nucleotide sequence. The genomic RNA of the virus was 5,964 nucleotides in length, excluding the 3'-terminal poly(A) tail. It contained five open reading frames (ORFs), consistent with other members of Potexvirus. The ORF sequences differ from those of previously reported potexviruses. Phylogenetic analysis indicated that the polymerase of the virus is closely related to that of strawberry mild yellow edge virus; and the CP, to those of both yam virus X and vanilla virus X. We propose that this virus be designated as "cnidium virus X" (CnVX).