The C 4 pathway is found in 62 lineages of land plants. We assess evidence for parallel versus convergent evolution of C 4 photosynthesis from three approaches: (i) studies of specific genes and cis-elements controlling their expression; (ii) phylogenetic analyses of mRNAs and inferred amino acid sequences; and (iii) analysis of C 3 and C 4 genomes and transcriptomes. Evidence suggests that although convergent evolution is common, parallel evolution can underlie both changes to gene expression and amino acid sequence. cis-elements that direct cell specificity in C 4 leaves are present in C 3 orthologues of genes recruited into C 4 , probably facilitating this parallel evolution. From this, and genomic data, we propose that gene duplication followed by neofunctionalisation is not necessarily important in the evolution of C 4 biochemistry.