There are about 40 species in the Mediterranean genus Origanum, most of them low, shrubby inhabitants of rocky places. The name comes from the Greek for “joy (or ornament) of the mountains,” though we have no evidence about how the Greeks enjoyed it. Oregano was little known in the United States until the rise of the pizza after World War II. Oregano species easily form hybrids with each other, so it’s not easy to sort out identities. The important thing for the cook is that they come in a range of flavors, from mild to strong and penetrating. The penetrating quality comes from the phenolic compound carvacrol. Greek oreganos are typically rich in carvacrol, while milder Italian, Turkish, and Spanish oreganos contain more thymelike thymol and fresh, green, floral, and woody terpenes.