Bupleurum L., with ca. 150 species, is one of the largest genera in the Apiaceae (Umbelliferae). The genus has a broad distribution in the Northern Hemisphere, and it is represented in North America by the native and possibly endemic species Bupleurum americanum J.M. Coult. & Rose, and by three introduced species: B. lancifolium Hornem., B. rotundifolium L., and B. odontites L. Here we report the occurrence of a new alien species of the genus in North America: Bupleurum gerardii All. We present a general characterization of the species and discuss the possible origin of the populations that have been found in Tennessee and Virginia. In addition, we confirm the records of B. odontites for the states of Maryland, Massachusetts and Oregon. All previous citations of B. odontites in Virginia refer to material of B. gerardii. The history of the discovery of this species in North America suggests that the treatment of sparingly naturalized taxa in floras is erratic and identifications of these species suspect.