The speciation process within plant families has been asymmetrical, consisting of a small and a large group. I studied this pattern within the cabbage family (Brassicaceae), with a focus on the smaller group Aethionemeae. Combining the latest sequencing techniques, herbarium material and greenhouse experiments I tried to understand the evolution of Aethionema species varying from a species to trait evolution. For example: the phylogeny of Aethionema helped us to assess that the ancestral area of this genus is probably the Irano-Turanian region and greenhouse assessments showed us that the genomic locations of chemical defence compounds of Aethionema correlate with a sulphate transporter gene and a flowering time gene. These findings are a start to understand the underlying mechanisms of the asymmetrical speciation pattern seen through the major plant families.