Taxonomic revision of Saundersella (Ectocarpales s.l., Phaeophyceae) from the northwestern Pacific with description of Saundersella crassa sp. nov. and transfer of Heterosaundersella hattoriana to Saundersella

Abstract

ABSTRACT Saundersella crassa sp. nov. (Ectocarpales s.l., Phaeophyceae) is newly described from cold-water regions of Japan and the northern Pacific. Saundersella crassa is similar to S. simplex (generitype) in morphology and has been identified as S. simplex in the area, but it has longer and thicker thalli, grows on different basiphytes (S. crassa on Chordaria spp vs S. simplex on Analipus spp) and is genetically distinct in the mitochondrial cox3 and chloroplast atpB, psaA, psbA and rbcL DNA sequences. The erect thalli of S. crassa were simple, filiform, soft and gelatinous, solid when young but later becoming hollow, cord-shaped, attenuated at the base to an indistinct stipe, at times twisted, yellowish to olive brown, and up to 50(–90) cm long and 5 mm wide. The erect thalli were composed of multiaxial colourless central medullary filaments and pigmented assimilatory filaments of 2–6 cells. Terminal cells of the assimilatory filaments were large and swollen, spherical or obovate. Unilocular zoidangia were sessile and obovate or irregular in shape, and were formed on erect thalli at the end of medullary cells or at the base of assimilatory filaments. In the molecular phylogeny, the type of the genus Heterosaundersella, H. hattoriana, was sister to S. crassa and was nested in the clade composed of S. simplex and S. crassa, irrespective of their differences in the habit and occurrence of basal prostrate thalli forming plurilocular zoidangia. Therefore, we propose the new combination S. hattoriana comb. nov. for H. hattoriana. Heterosaundersella thus becomes a taxonomic synonym of Saundersella.