Polyploidization has been a critical force in the diversification of flowering plants. Allopolyploidy, involving hybridization coupled with whole genome duplication, results in offspring having the complete diploid chromosome complements of each parent. As such, it effects reproductive isolation and facilitates speciation; allopolyploidy has also been shown to lead to adaptation to new landscapes and range expansion. Genus Eutrema (Brassicaceae) is an excellent study system to better understand allopolyploid origins. Eutrema has received a great deal of attention in the systematics literature, includes well-studied model species, and exhibits cytotype variation both within and among lineages. The near circumarctic Eutrema edwardsii, which comprises tetra-, hexa-, and octoploids of allopolyploid origin, is particularly well-documented across its range. A progenitor-derivative relationship for E. edwardsii has recently been documented with the federally listed Colorado endemic E. penlandii, a diploid species from which E. edwardsii is highly disjunct. However, it is suspected that an additional 1-2 diploid progenitors exist for tetraploid and hexaploid populations of E. edwardsii. Although no other diploid species have been described from the E. edwardsii complex, recent evidence from flow cytometry provides evidence for a cryptic taxon from Nunavut, Canada. The goal of our research is to further document phylogenetic relationships among the diploid species of Eutrema, while providing additional insight into the allopolyploid origin of E. edwardsii.