An updated molecular phylogeny of Polygonoideae (Polygonaceae): relationships of Oxygonum, Pteroxygonum, and Rumex, and a new circumscription of Koenigia.
Many Polygonaceae are primary successors or "weedy" and Aconogonon polystachyum and species and hybrids of both Emex and Reynoutria are pernicious invasives outside their native ranges. Polygonaceae have a particularly muddled taxonomic history and despite ongoing systematic studies, there are still large-scale questions about evolutionary relationships within the group. In this study, we address the relationships of Aconogonon, Emex, Fallopia, Koenigia, Oxygonum, Polygonum, and Rumex. We clarify the evolutionary history of Polygonoideae by building on an existing molecular dataset (nrITS, matK, trnL-trnF) analysed with maximum likelihood and Bayesian methods. Results indicate that the African Oxygonum is an isolated lineage likely sister to all other members of Polygonoideae, the two species of Emex are nested in the Rumex clade, Fallopia and Koenigia are polyphyletic with Aconogonon and Koenigia forming a clade, and Fallopia denticulata and F. cilinodis are separate from the Fallopia s.str. clade. Relationships within the Polygonum clade reflect geographic distribution with a North America clade sister to a clade containing cosmopolitan and Central Asian species. Based on these findings, we recognize Oxygoneae and Pteroxygoneae as tribes, include Aconogonon within Koenigia, and merge Emex with Rumex. Formal descriptions and nomenclatural changes are provided.