A taxonomic study of JapaneseScytosiphon(Scytosiphonales, Phaeophyceae), including two new species

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Abstract
SUMMARY: Morphological and culture studies were carried out on the genusScytosiphon(Scytosiphonales, Phaeophyceae) growing in Japan. Morphologies of plurilocular zo‐idangia and sporophytic thalli were found to be useful as taxonomic characters. Two types of plurilocular zo‐idangial sori were recognized: (i) loosely coherent plurilocular zoidangia without a cuticular layer (loose type); (ii) tightly coherent plurilocular zoidangia with a cuticular layer (coherent type). The sporophytic thallus morphology was different among species in general appearance (tufted or discoid), degree of cohesion of erect filaments, and presence or absence of paraphyses. Two new species are described,Scytosiphon gracilissp. nov. andScytosiphon tenellussp. nov,Scytosiphon gracilisis distinguished from other species by a thin medullary layer, coherent plurilocular zoidangia, no ascocysts associated with plurilocular zoidangia, and Compsonema‐like sporophytic thalli.Scytosiphon tenellusis characterized by a thin medullary layer, coherent plurilocular zoidangia, ascocysts among plurilocular zoidangial sori, andStragularia‐like sporophytic thalli.Scytosiphon lo‐mentaria(Lyngbye) Link is characterized by a constricted gametophytic thallus, loose plurilocular zoidangia, the presence of ascocysts, and sporophytic thaili identified withMicrospongium gelatlnosumReinke.