The paper describes a new taxon, Juncus bulbosus f. submucronatus J. Proćków, designates an epitype for J. bulbosus L. f. bulbosus, and details the distribution of both forms. The new form is native to most of Europe, NW Africa and Azores, and introduced to E Canada, SE Australia and S Chile. It is more frequent in western, central (excluding Poland) and southern Europe, contrary to f. bulbosus which is more common in northern Europe (excluding Iceland and Faroe Islands) and in Poland. A detailed key to all the infraspecific taxa of J. bulbosus is given. The new taxon differs from its closest relatives by the presence of dorsal (i.e. localised just below the apices of perianth segments) mucros usually pronouncedly or at least distinctly exceeding the perianth tops. The chromosome number for the new taxon (2n = 40) and ecological differences between the forms are given. In Poland f. submucronatus grows in eutrophic ponds and f. bulbosus thrives in oligotrophic Lobelia lakes.