Carex secalina, a species native to eastern Europe and Asia, is reported as a new naturalized member of the North America flora. There are currently seven known populations in North America, all in southeastern New York State. In its native range, it is a species of damp or wet, often saline soils. In North America, it is known to grow predominately in highly disturbed urban habitats, including areas influenced by salt. It currently does not appear to be invasive in North America, but further monitoring is warranted due to its high potential fecundity. The updated Köppen-Geiger climate classification model is used to assess potential regions in North America where C. secalina might grow. Carex secalina is easily distinguished from all other members of the North American flora by a combination of the perigynia being very sharply two-angled and the spikes being pedunculate, especially proximally. Images of the species and its habitat in North America are presented, as are maps showing its distribution in its native and introduced ranges.