Colinear mitochondrial gene clusters across angiosperms. The cladogram above shows the phylogenetic relationships among these sequenced mitochondrial genomes . Gray rectangles denote the presence of a gene cluster, even if one of the genes is a pseudogene. Clusters composed of more than two genes are split into two-gene subclusters and boxed together, with the common gene of both in bold. In the case of the four gene cluster rpl2-rps19-rps3-rpl16, there are two two-gene subclusters, which themselves can be colinear. In these cases, a vertical bar connects the two gray rectangles in the right panel. In the top panel are clusters inferred to have been present in the common ancestor of angiosperms. The bottom three panels show clusters inferred to have been present in the common ancestor of eudicots or monocots, but not in the ancestral angiosperm. The bottom panel contains clusters where the genes involved are encoded on opposite strands in the genome, whereas all clusters in the top three involve genes on the same strand and orientation. Genes in the bottom panel are noted as being in the forward strand (>) or reverse strand (<).