What is Kalonji a.k.a The Black Seeds ?
Kalonji are the seeds obtained from an annual flowering herb known as Nigella Sativa. Nigella sativa, the most well-known member of the genus Nigella, grows 8-35 inches (20-90 cm) in height and has finely divided, somewhat threadlike leaves. This species has pale-blue to pale-purple flowers that bloom in the spring and produce seed capsules (fruit) that contain numerous black seeds. It belongs to the family Ranunculaceae.
The genus likely originated in parts of the eastern Mediterranean, northeastern Africa, and southwestern Asian regions. Nigella sativa is found growing wild in regions of northern Africa,Turkey, Syria, Iraq, and Iran. The species is also cultivated on a commercial scale in northern Africa (Egypt,Tunisia,Sudan), eastern Africa (Ethiopia), western Asia (Iraq, Israel, Jordan, Lebanon,Syria,Turkey,Yemen), and southern Asia (India,Iran,Pakistan).
What are Onion seeds ?
Onion seeds are obtained from the species Allium Sepa L. The species Allium cepa L., commonly known as onion belongs to the family Amaryllidaceae, subfamily Allioideae. A. cepa is a biennial plant with adventitious and fibrous roots and 3–8, distichous, glaucous leaves. The bulb is made of concentric, enlarged fleshy leaf bases. The outer leaf base dries and becomes thin and variously coloured, forming the protective coat, while the inner leaf bases thicken when the bulb develops. The mature bulb can be globose, ovoid or elongate and its size varies depending on the cultivar. A. cepa is widely cultivated in almost every country of the world.
Why the confusion ?
The majority of people get confused because both the seeds are black in color and are somewhat similar in the size and appearance. But if you look closely they are very different. Here's a comparative photograph of Kalonji and Onion seeds.
The left image shows Kalonji seeds which are triangular in shape whereas the right image depicts onion seeds having a oval and irregular shape.
Kalonji seeds have been regularly used in Indian cuisines for the preparation of traditional pickles and for sprinkling on Persian Breads.