Hybrid Mustard Seed, scientifically known as Brassica rapa subsp. oleifera, is field mustard. Black mustard is Brassica nigra, while brown mustard is Brassica juncea. Use escarole, gai choy, kale, radish greens, spinach, or Swiss chard as alternative greens in recipes. Mustard greens, also called curly or curled mustard, mustard spinach, Indian mustard, or leaf mustard, are versatile. Mustard seeds, categorized by color (yellow, brown, or black), are produced by plants in the Brassicaceae family, encompassing both Brassica and Sinapis genera.