This widespread northern and western (circumboreal) species of wet sites is rare in most of the Ohio Valley. However, it has been reported from all adjacent states, with a cluster of records from s. Ill. (FNA 24, K). The single Ky. record is a verified coll. from CARL (MUR): L.M. Wilson #1568. The more northern (circumboreal) perennial, A. geniculatus L., is closely related, with 2n = 28 (versus 14 or 28 in aequalis). A. geniculatus has been erroneously reported from Ky. (Short et al. 1833; Gm; Anderson 1924), apparently based on early taxonomic confusion.