The mustard family Brassicaceae (also known as Crucifers, from the cross-like form of their flowers) comprises ca. 4000 species, including economically important crops such as cabbage and canola, many species adapted to extreme environments, noxious weeds, and the model plant Arabidopsis thaliana. Despite their importance, the relationships among major lineages in the family have remained unresolved. This gap in our knowledge is an impediment for understanding the sequence of genetic events that led to trait diversity and the many ecological adaptations seen in this family of plants. Lack of such information can also slow down efforts towards sustainable crop improvement through transferring traits from one species into another by conventional or new breeding technologies.