The seeds are usually about 1 to 2 millimetres (0.039 to 0.079 in) in diameter and may be colored from yellowish white to black. They are an important spice in many regional foods and may come from one of three different plants: black mustard (Brassica nigra), brown Indian mustard (B. ... hirta/Sinapis alba).
Brassica nigra, or black mustard, is an annual plant cultivated for its black or dark brown seeds, which are commonly used as a spice. It is native to tropical regions of North Africa, temperate regions of Europe, and parts of Asia.