Genetic distinctness and phylogenetic relationships among <i>Undaria</i> species (Laminariales, Phaeophyceae) based on mitochondrial <i>cox</i>3 gene sequences

Abstract

SUMMARY Genetic relationships among Undaria species and among populations of each species were studied based on DNA sequences of the mitochondrial cox 3 gene. Although three Undaria species, U. peterseniana (Kjellman) Okamura, U. pinnatifida (Harvey) Suringar and U. undarioides (Yendo) Okamura, have been described based mostly on blade morphology, plants with intermediate morphologies have also been found. Multiple plants from several populations in Japan were collected. Morphological characters could identify most of the samples unambiguously. A few samples with intermediate morphologies were also collected. Mitochondrial haplotypes found in each population were different for each identified species, and each species had multiple haplotypes. In the cox 3 haplotype network analysis, the numbers of steps between haplotypes within and between species were similar, and haplotypes of each species did not group together. The close genetic relationships among species strongly suggest that these species are conspecific. Alternatively, recent speciation could be possible with maintenance of ancestral polymorphisms within the species (i.e. incomplete lineage sorting). Haplotypes of samples with intermediate morphologies were different for each sample and the same as ones found in the local population, suggesting interspecific hybridizations among species.