A new phylogeny of Rumex (Polygonaceae) adds evolutionary context to the diversity of reproductive systems present in the genus

Rumex is a unique member of the Polygonaceae family of plants. A source of
intrigue for Rumex lies in the diversity of the reproductive systems
associated with this genus. Four previously circumscribed subgenera and
some two-hundred species comprise the collective Rumex genus. These
species exhibit monoecious, dioecious, synoecious (hermaphroditic), and
polygamous reproductive systems. Moreover, some of the dioecious species
contain heteromorphic sex chromosomes, a phenomenon that is very rare in
angiosperms. Apart from these confirmed morphological and
phytogeographical distinctions, two of the four described subgenera, Rumex
subg. Acetosa and Rumex subg. Acetosella, are distinctive in their sex
chromosome systems. For this study, we used three chloroplast markers,
rbcL, trnH-psbA, trnL-F, and dense taxon sampling, to reconstruct the most
comprehensive molecular phylogeny of Rumex to date. The reconstructed
phylogeny for this work resolves six major clades and one large grade in
Rumex subg. Rumex. In addition, the species with known dioecious
reproductive systems are resolved within a broader clade termed “the
dioecious clade”. These results suggest that the species with divergent
reproductive systems are more closely related to each other than to other
species comprising the rest of the Rumex genus. Furthermore, some species
with known synoecious reproductive systems are resolved in a single clade
which is also nested within “the dioecious clade”. These results imply a
possible reversal occurring over time which suggests the highly plastic
nature of the reproductive systems in Rumex species.