Abstract:
DNA sequence data have become a crucial tool in assessing the relationship between
morphological variation and genetic and taxonomic groups, including in the Antarctic biota.
Morphologically distinct populations of submersed aquatic vascular plants were observed on
sub-Antarctic Marion Island, potentially representing the two species of such plants listed in the
island's flora, Limosella australis R.Br. (Scrophulariaceae) and Ranunculus moseleyi Hook.f.
(Ranunculaceae). To confirm their taxonomic identity, we sequenced a nuclear locus (internal
transcribed spacer; ITS) and two plastid loci (trnL-trnF, rps16) from three specimens collected on
Marion Island and compared the sequences with those in public sequence databases. For all three
loci, sequences from the Marion Island specimens were nearly identical despite morphological
dissimilarity, and phylogenetic analyses resolved them to a position in Limosella. In phylogenetic trees
and comparisons of species-specific sequence polymorphisms, the Marion Island specimens were
closest to a clade comprising Limosella aquatica L., L. curdieana F.Muell. and L. major Diels for ITS
and closest to L. australis for the plastid loci. Cytonuclear discordance suggests a history of
hybridization or introgression, which may have consequences for morphological variability and
ecological adaptation.
