- You will get 1000 Seeds of Black Mustard Garden Heirloom Non-GMO Vegetable Seeds. - Genus: Brassica. - 1,000 Black Mustard Seeds Garden Heirloom Non-GMO. - Brassica nigra, or black mustard, is an annual plant cultivated for its dark-brown-to-black 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.