Keys, illustrations, descriptions, and ecological notes are provided for nine species ofPolysiphoniafrom Scandinavia:P. arctica, P. brodiaei, P. elongata, P. hemisphaerica, P. lanosa, P. nigra, P. nigrescens, P. urceolata, andP. violacea. Taxonomical and nomenclatural questions are discussed with special reference to the application of the specific epithetviolacea. On the basis of examination of type material,P. fibrillosais considered conspecific withP. violacea, as this species is currently circumscribed, while the entity to which this name was originally applied is probably the same asP. nigrescensandP. fucoides.