Yuzu (Citrus junos Sieb. Ex Tanaka) is one of the most important Citrus species in China, Japan, and Korea. Yuzu is assumed to be a natural hybrid. However, concrete evidence supporting its hybrid origin has not been reported yet. To identify putative maternal species, the nucleotide sequences of five hypervariable regions covering 17,531 bp in citrus chloroplast genomes were obtained from yuzu. A phylogenetic tree based on these sequences showed that yuzu was most closely related to Ichang papeda (C. cavaleriei), suggesting that Ichang papeda might be a seed parent of yuzu. To identify paternal species, yuzu homologs of 103 single-copy genes found among citrus genomes were identified from a yuzu transcriptome that was de novo assembled using RNA-seq reads. Eighty homologous genes were identified from the yuzu transcriptome. A phylogenetic tree based on nucleotide sequence variations in 80 single-copy genes of yuzu and other Citrus species showed that yuzu was most closely related to mandarin. To assess hybrid origins of 80 single-copy genes, single nucleotide polymorphisms (SNPs) among yuzu, Ichang papeda, mandarin, citron, and pummelo were analyzed, and yuzu SNP genotypes were identified by visual investigation of alignments of RNA-seq reads. Forty-three out of 80 genes were assumed to originate from hybrids between Ichang papeda and mandarin. Taken together, results of this study indicate that Ichang papeda and mandarin might be the parental species of yuzu.