The Brassica genus includes broccoli, cabbage, cauliflower, turnips and radishes. The mustard family also includes plants grown for their leaves, like arugula, a number of Oriental greens, as well as mustard greens. Three related species of mustard are grown for their seeds:
Yello Mustard (Brassica alba or Brassica hirta) is a round hard seed, beige or straw coloured. Its light outer skin is removed before sale. With its milder flavour and good preservative qualities, this is the one that is most commonly used in ballpark mustard and in pickling.
Black Mustard (Brassica nigra) is a round hard seed, varying in colour from dark brown to black, smaller and much more pungent than the white.
Brown ustard (Brassica juncea) is similar in size to the black variety and vary in colour from light to dark brown. It is more pungent than the white, less than the black.