Molecular phylogeny of Punctaria mageshimensis reveals evidence for its transfer to Spatoglossum as S. mageshimense (Dictyotales, Phaeophyceae)

摘要

Taxonomy of the little-studied brown algal species Punctaria mageshimensis (Ectocarpales s.l.) was reexamined by molecular phylogeny and morphology. In the genetic analyses of newly collected specimens using plastid rbcL and psaA gene sequences, the specimens morphologically referable to P. mageshimensis were phylogenetically distant from Ectocarpales s.l. and were included in the clade of Spatoglossum (Dictyotales). Morphological reexamination of the type specimen and newly collected specimens confirmed its systematic position in Dictyotales: Branched thallus; cushion-shaped rhizoidal holdfast occasionally forming secondary holdfast at the bottom of the thallus; many discoidal plastids without pyrenoid per cell; tetrasporangium-like reproductive structures with dark, homogeneous cell content; occurrence of hair tufts. Genetically P. mageshimensis was most related to a reported sequence of Spatoglossum asperum, but P. mageshimensis was considerably different from S. asperum as well as other known Spatoglossum species in the deep habitat and in having scarcely-branched lanceolate and considerably thickened thallus. In conclusion, we propose the transfer of P. mageshimensis to Spatoglossum as S. mageshimense comb. nov.