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

Morphological and culture studies were carried out on the genus Scytosiphon (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 gracilis sp. nov. and Scytosiphon tenellus sp. nov, Scytosiphon gracilis is distinguished from other species by a thin medullary layer, coherent plurilocular zoidangia, no ascocysts associated with plurilocular zoidangia, and Compsonema-like sporophytic thalli. Scytosiphon tenellus is characterized by a thin medullary layer, coherent plurilocular zoidangia, ascocysts among plurilocular zoidangial sori, and Stragularia-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 with Microspongium gelatlnosum Reinke.