Red Onion Seeds

"Onion seeds" usually refer to Kalonji (Nigella seeds), small black seeds from the Nigella sativa plant, used in cooking for their pungent, slightly bitter, oniony flavor, but they are not the seeds from the common onion (Allium cepa). True onion seeds come from the flower stalk of an onion plant grown for two years, are black and irregular, and can be used for planting or as a spice, though less common than Kalonji. The confusion arises because Kalonji has a mild onion aroma when crushed, leading to the mislabeling in spice aisles.