Taxonomic revision of Tinocladia (Ectocarpales s.l., Phaeophyceae): merger of Tinocladia with Eudesme and description of E. pseudocrassa sp. nov

ABSTRACT A molecular phylogeny of Tinocladia and Eudesme based on specimens covering a large proportion of the known species was done using mitochondrial cox1 and cox3, chloroplast atpB, psaA, psbA and rbcL genes and 5.8S rDNA and its ITS2 region sequences. The phylogeny revealed a close phylogenetic relationship between the two genera and the occurrence of a cryptic species within the generitype T. crassa. Eudesme species (E. borealis, E. shandongensis and the generitype E. virescens) showed a sister relationship with the northern hemisphere Tinocladia (T. crassa, including a cryptic sister species T. pseudocrassa sp. nov., and T. sanrikuensis), whereas southern hemisphere Tinocladia (T. australis, T. falklandica, T. novae-zelandiae, and a cryptic species from New Zealand) nested in the Eudesme clade. Morphologically, Tinocladia species have been distinguished from Eudesme by their denser medullary filaments and more extensive subcortical layer, but our molecular phylogenetic analyses suggest that these features do not correlate with genetic differences. The cox3 sequence divergence between northern hemisphere Tinocladia and the lineage that includes Eudesme and southern hemisphere Tinocladia was comparable to or smaller than those within selected ectocarpalean genera. We therefore propose to merge Tinocladia with Eudesme and resurrect Eudesme crassa (Suringar) Okamura for T. crassa. Although the two independent lineages of T. crassa do not show marked morphological differences, they are genetically isolated even in sympatric populations. We therefore propose to treat them as independent species. In this paper we neotypify Tinocladia crassa (=Eudesme crassa), describe E. pseudocrassa sp. nov., and determine that the Californian population of E. crassa is an introduction from Northeast Asia. HIGHLIGHTS •A taxonomic revision of Eudesme and Tinocladia, based on genetic and morpho-anatomy, provides evidence to merge Tinocladia with Eudesme. •The finding of cryptic species in New Zealand highlights the need for further taxonomic studies in this region. •The genetic data have revealed the occurrence of a cryptic species within T. crassa in Japan.