Plant Systematics and Evolution 304: 757-762.
Brassicales comprise 17 families, c. 400 genera and more than 4600 species. Despite the mustard family (crucifers, Brassicaceae) continuing to be the subject of intensive research, the remaining 16 families are largely under studied. Here I summarize the available data on chromosome number and genome size variation across Brassicales in the context of a robust phylogenetic framework. This analysis has revealed extensive knowledge gaps in karyological data for non-crucifer and species-rich families in particular (i.e., Capparaceae, Cleomaceae, Resedaceae and Tropaeolaceae). A parsimonious interpretation of the combined chromosomal and phylogenetic data set suggests that the ancestral pre-Brassicales genome had 9 or 14 chromosome pairs, later multiplied by the At-β (beta) whole-genome duplication (WGD) to n = 18 or 28. This WGD was followed by post-polyploid diploidization marked by diversiication to 12 or 13 families and independent decreases in chromosome numbers. Family-specific WGDs are proposed to precede the diversiication of Capparaceae, Resedaceae and Tropaeolaceae.