Mace spice is a dried, outer aril, enveloping firmly around the nutmeg kernel. Nutmeg kernel and mace arils indeed are two separate spice products of same nutmeg fruit. However, mace characteristically compose higher concentration of certain essential oils and features refined yet intense aroma than nutmeg. For the same reasons, it commands higher price and special place in the kitchen spice box!
Mace as well as the nutmeg seeds were thought to have originated in the tropical rain forest of Indonesian Maluku Islands, also known as the spice Islands. Binomially, nutmeg is evergreen tree belonging to Myristicaceae family, and known scientifically as Myristica fragrans. There are several species of nutmeg grown all over the world other than Myristica species, such as M. argentea, M. malabarica (Indian), and M. fatua. They are rather similar to M. fragrans in appearence, however, inferior to in flavor and aroma.