Phylogeny of Alariaceae (Phaeophyta) with special reference to Undaria based on sequences of the RuBisCo spacer region

In order to investigate the phylogenetic relationships of the family Alariaceae, we determined the complete sequences of the plastid RuBisCo spacer region for fourteen taxa of the Alariaceae and for two reference species. The RuBisCo spacer sequences showed that the Alariaceae forms two clades: one comprises Alaria, Pterygophora and Undaria, while the other comprises Ecklonia, Eckloniopsis, Eisenia, Egregia and Laminaria. These results favour the narrow concept of the Alariaceae, in which Alaria, Pterygophora and Undaria only may be placed. Ecklonia, Eckloniopsis, Eisenia, Egregia and Laminaria appear not to have a common ancestor. The RuBisCo spacer sequences of the three Undaria species also indicate that the species are very closely related, with an intermediate relationship at the DNA level; we hypothesize that there might be a reticulate evolution among the species. In this scenario, U. undarioides might be an ancient hybrid species from the parental species of U. peterseniana and U. pinnatifida. The RuBisCo spacer region, including its flanking areas, is useful for inferring phylogenetic relationships within the family Alariaceae.