Fennel seeds come from common fennel. These oblong, greenish-brown seeds are often confused with aniseeds, which are similar in flavor and appearance, but smaller.
Whole or ground, fennel seed is a common ingredient in both sweet and savory foods like Italian sausages, rye breads, and many liqueurs.
As with most seeds and spices, fennel seeds should be stored in a cool, dark place for no more than 6 months.