Mustard grows wild. Cabbage, broccoli, and cauliflower were bred from it.
Modern cabbage was bred from wild cabbage, known to the Romans.
Broccoli and cauliflower also came into human kitchens during roughly the same period, while mustard was known and cultivated centuries before.
What is apparently interesting about this genus is that it exhibits a property known as the Triangle of U - that all the varieties of the genus or family are reducible to three genomic species, of which they are all permutations.
In other words, they are three "species" or combinations thereof which are yet capable of easily interbreeding with one another and producing hybrids.
Yet macroevolutionary theory postulates that "species" are incapable of interbreeding and having fertile offspring.
It would seem that the Brassica genus demonstrates a postulate of the antimacroevolutionary movement - that living things are created according to their kinds or generes and that these kinds are stable in themselves.
Instead of a radical change over time into an enormous variety of incompatible species, the large and varied Brassica genus consists of three basic and highly compatible genomes.