A plastome phylogeny of Rumex (Polygonaceae) illuminates the divergent evolutionary histories of docks and sorrels

<p>The genus <em>Rumex</em> L. (Polygonaceae) provides a unique system for investigating the evolutionary development of sex determination and molecular rate evolution. Historically, <em>Rumex</em> has been divided, both taxonomically and colloquially into two groups: 'docks' and 'sorrels'. A well-resolved phylogeny can help evaluate a genetic basis for this division. Here we present a plastome phylogeny for 34 species of <em>Rumex</em>, inferred using maximum likelihood criteria. The historical 'docks' (<em>Rumex</em> subgenus <em>Rumex</em>) were resolved as monophyletic. The historical 'sorrels' (<em>Rumex</em> subgenera <em>Acetosa</em> and <em>Acetosella</em>) were resolved together, though not monophyletic due to the inclusion of <em>R. bucephalophorus</em> (<em>Rumex</em> subgenus <em>Platypodium</em>). <em>Emex</em> is supported as its own subgenus within <em>Rumex</em>, instead of resolved as sister taxa. We found remarkably low nucleotide diversity among the docks, consistent with recent diversification in that group, especially as compared to the sorrels. Fossil calibration of the phylogeny suggested that the common ancestor for <em>Rumex</em> (including <em>Emex</em>) has origins in the lower Miocene (22.13 MYA). The sorrels appear to have subsequently diversified at a relatively constant rate. The origin of the docks, however, was placed in the upper Miocene, but with most speciation occurring in the Plio-Pleistocene.</p>