Mustard seeds are the small round seeds of various mustard plants. The seeds are usually about 1 or 2 mm in diameter. Mustard seeds may be colored from yellowish white to black. They are important SPICES in many regional foods. The seeds can come from three different plants: black mustard (Brassica nigra), brown Indian mustard (B. juncea), and white mustard (B. hirta/Sinapis alba). The seeds for the mustard powder originated from the Andra Pradesh region of India.