Anise and fennel are both in the Apiaceae family of plants but they are in different genuses. Both are used as medicines and flavorings, and they taste similar to one another. The seeds of these two plants can often be used interchangeably in culinary dishes, but only fennel has edible leaves and stalks. Though they look similar, there are differences in these plants that make them easy to tell apart.
Known scientifically as Pimpinella anisim, anise grows to heights of 3 feet (0.9 meters) and has long stalks with feathery leaves. When it blooms, the anise plant is covered with small, white flowers that emerge from the ends of the stalks. Fennel, Foeniculum volgare, also grows on stalks with small, thin leaves, but the base of the plant is in the form of a bulb from which the stalks emerge. Small yellow flowers appear on the ends of the stalks, which can grow to heights of over 8.2 feet (2.5 meters).
Many of the similarities between anise and fennel are present because these plants are in the same family. They are also related to licorice, tarragon, carrots, celery, and hemlock, the last of which is extremely poisonous. Anise and fennel are both native to regions of Europe, Africa, and the Middle East that border the Mediterranean Sea, though anise also grows in throughout Asia.
Both anise and fennel may be eaten, but different parts of each plants are edible. In the case of anise, the small fruits and seeds may be eaten or dried and used as a spice. An oil can also be pressed from the fruit and used to give dishes a distinctive flavor, similar to that of licorice. Many parts of the fennel plant are edible. The leaves, seeds, stems and bulbs of the plant can be eaten raw or cooked and have a flavor that is similar to, though milder, than anise.
Medicinally, anise and fennel are used for very different purposes. Anise seeds have been used for thousands of years as a remedy for persistent cough, excessive gas, and bad breath. Any edible part of the fennel plant can be used as an anti-inflammatory, to treat stomach discomfort, or as a diuretic.