The "true" pearl onion (A. ampeloprasum var. sectivum or A. ampeloprasum 'Pearl-Onion Group') is a close relative of the leek (A. ampeloprasum var. porrum), and may be distinguished from common onions by having only a single storage leaf, similar to cloves of garlic. They are cultivated mostly in Germany, the Netherlands, and Italy; usually in home gardens, although formerly on a commercial scale. They are mostly used for pickling.
However, the majority of onions grown for pickling are common onions (A. cepa). They are grown to a small size suitable for pickling by planting at a high density.
Because of its uniquely diminutive appearance and a taste sweeter than that of a common onion, it has also been used in dishes ranging from mid-20th-century American casserole dishes such as succotash to sweetly flavored onion relishes in Indian cuisine. A pearl onion will take up to two years to become sufficiently sweet for sale (such is the main reason it is less popular in America than other onions). Pearl onions are, however, a staple to the cuisine of Northern Europe, especially Sweden.