The onion (Allium cepa), also known as bulb onion, common onion, or bulb onion, is the most widely cultivated species of the genus Allium, which includes several species commonly called onions and used in cooking, such as spring onion (A. fistulosum), Egyptian onion (A. × proliferum), and Canadian onion (A. canadense). Several Allium species are also known as wild onions. The vast majority of A. cepa cultivars belong to the common onion group (A. cepa var. cepa) and are generally referred to simply as onions. The Aggregatum group of cultivars (A. cepa var. aggregatum) includes shallots and seed onions.