Although they share a similar taste profile—reminiscent of black licorice—fennel and anise are two different plants. The botanical name of anise is Pimpinella anisum while the botanical name of fennel is Foeniculum vulgare. Both anise and fennel belong to the Apiaceae family.
In addition to the fact that they share a similar flavor, what often creates confusion among these two plants/foods is that fennel is often referred to as anise. Since the whole plant (bulb, stalks, fronds) of fennel is consumed while it is usually just the seeds from the anise plant that are eaten, if you see a vegetable-like plant called "anise," chances are that it is actually fennel.
There is one further complication to the anise and fennel story. Historically, several different plants have been referred to as "anise." One version of anise you may also be familiar with is star anise (also called Chinese anise). This form of anise gets its name from the eight-pointed star that forms a pod for its seeds. The seeds from star anise provide a very similar flavor to the Pimpinella plant described above, and they are commonly consumed in China and other parts of Asia where the tree that produces them commonly grows. Star anise has its own scientific name (Illicum verum) and unlike fennel and anise, it is not a part of the Apiaceae family but rather the Illiciaceae family.
For more information on this topic, please see: