The Brassicaceae (Cruciferae) or mustard family is a well-defined group of about 310 genera and some 3500 species distributed primarily in the temperate and alpine areas of all continents except Antarctia. It is most highly diversified in central and western Asia, Mediterranean Europe and western North America. This article discusses the economic importance of the family (food, oils, condiments, ornamentals and weeds) and role played by one of its weedy member, the model organism Arabidopsis thaliana, in the advancement of modern experimental biology. Here we also review the morphology, biogeography, ecology and phylogenetic relationship within Brassicaceae and to other families. We also cover the significance of molecular data in dividing the family into 48 monophyletic tribes and in determining its major lineages. Finally, a brief discussion is presented on the whole-genome duplication events and their possible role in the radiation and diversification of the family.

Key Concepts:

• Model organisms, such as the mustard Arabidopsis thaliana, should always be used to understand complex biological phenomena in other organisms.
  
• Owing to extensive morphological convergence, molecular data alone provide the most reliable and solid phylogenetic classification within the Brassicaceae.
  
• Invasive weeds of the mustard family can only be understood by closer studies of their immediate wild relatives.
  
• Germplasm conservation centres of the economically important Brassicaceae should substantially increase their efforts to save their rapidly disappearing wild relatives.
  
• Vegetable crops of Brassica should be thoroughly tested to determine their medicinal values in combating cancer and other diseases.