Variation in the absolute rates of silent substitution in plastid (green) and mitochondrial (red) genomes across diverse angiosperms. The tree was rooted on Cycas, which was subsequently removed for presentation clarity. Branch-specific absolute silent substitution rates (per billion years) for the mitochondrial and chloroplast genomes are in red and green, respectively. Rate estimates for Silene were taken from previously published reports [2, 48]. Confidence intervals of 95% derived from the error in estimating branch-specific synonymous substitution rates are given in Additional file 1: Table S3.