The Brassicaceae (Cruciferae), or mustard family, are a cosmopolitan monophyletic group of 338 genera and 3709 species (Warwick et al., 2006c) distributed on all continents except Antarctica, especially in the temperate, alpine, and arctic regions. The family is most abundant in the Northern Hemisphere, with the major diversification center in the Irano-Turanian region (ca. 950 native spp.), and secondary centers in the Mediterranean region (ca. 600 spp.) and western North America (ca. 650 spp.). In the Southern Hemisphere, the family is less speciose and is most common along the high Andes from Colombia to Patagonia (ca. 350 spp.), and only a little over 100 species are indigenous to Australia and southern South Africa (Al-Shehbaz, 1984). Only three genera, Cardamine Linnaeus, Lepidium Linnaeus, and Rorippa Scopoli are represented by native species on all contents. Although less than a dozen species are adapted to aquatic habitats, the vast majority of species grow in arid or mesic areas and only a few reach elevations as high as 6,400 m (e.g., the Tibetan Lepidostemon everestianus Al-Shehbaz).

The Brassicaceae are well defined morphologically and can easily be distinguished by the cruciform corolla (four separate petals in the form of cross, hence the name Cruciferae), often six tetradynamous stamens (inner four longer than outer two), capsular fruits with a septum dividing it into two chambers, and folded embryos. There are, however, a few exceptions to this general morphological combination. All members of the family release the pungent mustard oils (isothiocyantes) upon crushing the fresh parts.

This introductory part is intended to orient the reader to brief information on various aspects of the family and to direct her/him to key references that provide more detailed accounts on a given subject. For extensive surveys of the family, the following reviews and monographs are recommended: Hayek (1911), Schulz (1936), Hedge (1976), Al-Shehbaz (1984), Appel & Al-Shehbaz (2003), Koch et al. (2003), Al-Shehbaz et al. (2006), Koch & Al-Shehbaz (2009).