Molecular data support the recognition of three monophyletic families, Capparaceae s. str., Cleomaceae, and Brassicaceae, instead of an all-encompassing Brassicaceae or a paraphyletic Capparaceae s.l. This view is reinforced with many figures showing two basic and ubiquitous differences in cleomoid seed structure. First, the more or less strongly incurved seed, varying from reniform to horseshoe-shaped, coiled or conduplicate, uniformly and in all species, results in a deep invagination of the testa (the cleft) projecting into the interval between the two ends, or claws, of the embryo (this invagination is absent or rarely reduced and atavistic in Brassicaceae, and infrequent in Capparaceae s. str., i.e., in some Capparis L. species and Crateva L., sister genus to all remaining Capparaceae s. str.). Second, the uniformly semicylindric, strictly incumbent cotyledons are small and narrow, but are never foliaceous and interfolded, circinate or convoluted, or massive and thick, as in the often accumbent, rarely incumbent Capparaceae, or as variable as in Brassicaceae. An illustrated glossary of Cleomaceae seed morphology, as well as depictions of Capparaceae, Cleomaceae, and Brassicaceae seeds and their sectional views, and a key to all three families, are included.