Juncus effusus s. str. has two native representatives on the coast of western North America. A new combination is provided for Juncus effusus subsp. pacificus, ranging from California to British Columbia. Juncus effusus subsp. austrocalifornicus is newly described from southernmost California, Arizona, and Baja California, México. It differs from subsp. pacificus by its pale sheaths, with less thickened and less overlapping margins, and its disjunct distribution. A key is provided for the subspecies of J. effusus in North America.