The taxonomic status of members of the genus Lepidium in the Intermountain West has been in flux for years. Species concepts and classification of these endemic species from the western United States center on the highly variable L. montanum complex. Until recently, classification treatments that use morphological features in this group have been adequate, but as new species are discovered and more locations reported, the limited number of morphological features available for classification and defining species concepts has led to more uncertainty about taxonomic rankings. As part of a molecular and morphological-based treatment of the group, flow cytometry was used to evaluate 58 collections of Lepidium from the Intermountain West. The ploidy level for 14 species and 11 varieties of Lepidium was surveyed to assess whether ploidy levels affected the interpretation of taxonomic rankings. Of the Lepidium taxa surveyed, 90% were tetraploid, and several were diploid and hexaploid. Tetraploid occurrences crossed all major species and varieties. No geographic distribution or habitat patterns were associated with ploidy level.