Streptanthus petiolaris was treated by other North American authors under Arabis, but the species does not belong to that genus (I. A. Al-Shehbaz 2003b) or to Boechera; it has 2n = 28, a chromosome number universal in Streptanthus and not found in any species of Arabis or Boechera, and it lacks the branched trichomes characteristic of those genera.