Molecular phylogeny and biogeography of Ecklonia spp. (Laminariales, Phaeophyceae) in Japan revealed taxonomic revision of E. kurome and E. stolonifera

Abstract

ABSTRACT Species level taxonomy and genetic structures of local populations of Ecklonia species (Laminariales, Phaeophyceae) distributed in northeastern Asia were examined using multigene molecular phylogeny of mitochondrial atp8–16S rDNA, cox1 and cox3, plastid atpB, psaA, psbA and rbcL gene sequences, and nuclear microsatellite markers. Japanese Ecklonia formed three to four clades with high to medium support (Groups 1, 2a, 2b, and 3). Group 1 was composed of morphospecies of E. radicosa with full statistical support. Groups 2a, 2b, and 3 were distinct but genetically close, and support for each clade was weak. Those genetic groups had distinct distributions, with some overlaps in contact regions in the Seto Inland Sea and vicinity. Microsatellite analyses suggested genetic exchange between Groups 2b and 3 in their contact region. In conclusion, E. radicosa was revealed to be an independent species, and synonymy between Eckloniopsis and Ecklonia was supported. In contrast, the independence of morphospecies E. cava, E. kurome, and E. stolonifera at species level was not supported. Instead, three genetic groups with separate distributional ranges were revealed. Therefore, we propose recognising E. cava, E. kurome, and E. stolonifera as a single species, and treating those three genetic groups as subspecies of E. cava, i.e. E. cava ssp. cava, E. cava ssp. kurome, and E. cava ssp. stolonifera. Furthermore, depending on the occurrence of stolons forming new sporophytes, i.e. rhizomatous holdfasts, two varieties, var. stolonifera and var. kuromeoides, are proposed in E. cava ssp. stolonifera.