Fennel is a native of the Mediterranean and southwest Asia; like dill, it has fibrous leaf stalks but feathery, tender leaves. There is one species of fennel, Foeniculum vulgare, and it comes in three different forms. The wild subspecies, piperitum, is sometimes collected from the countryside in southern Italy and Sicily, where it’s known as carosella and valued for its sharpness in meat and fish cooking. (Fennel now grows wild throughout central California as well.) The cultivated subspecies vulgare is known as sweet fennel thanks to its far richer content of the phenolic compound anethole, which is 13 times sweeter than table sugar, and also gives the characteristic sweet aroma of anise. And a specialized variety of sweet fennel, var. azoricum, develops the enlarged leaf-stalk bases of bulb or Florence fennel, which is used as an aromatic vegetable.