Evidence for allopolyploid speciation in Nymphoides (Menyanthaceae)

The floating-leaved aquatic plant genus Nymphoides includes diploid and polyploid species that are distributed worldwide. Prior studies found widespread incongruence between nuclear and plastid phylogenies, and this has prevented the construction of a unified phylogenetic hypothesis for the genus. In order to examine whether phylogenetic incongruence resulted from ancestral polyploidization events, we obtained DNA sequence data from two nuclear loci, phytoene desaturase (PDS) and transmembrane nine (TMN1), as well as the plastid trnT-trnF region. Multiple divergent copies of the nuclear genes were recovered from several species, and species with the most divergent copies were inferred to have originated through allopolyploidization. Our data support a scenario in which three groups of species descended from allopolyploidization events: a clade of North American species (N. aquatica and N. cordata), a clade of neotropical species (N. fallax, N. grayana, and N. humboldtiana), and the Aust...