Nutmeg trees are the only plant to give us two spices. (As opposed to a plant like dill which gives us a spice and an herb.)
Nutmegs are the actual seeds of the tree while mace is what is known as an airl—the protective coating of the seed.
Mace’s flavor and aroma differ slightly from nutmeg as its profile tends to be sharper and less sweet. It still carries distinct flavors of nutmeg, but with subtle notes of pine, black pepper, and coriander-like citrus.