Both are found on the same plant. The nutmeg is the inner kernel of the fruit. When ripe, the fruit splits open to reveal bright red arils which lie around the shell of the nutmeg - and once dried are known as mace blades. The flavor of both spices is very similar - warm, sweet and aromatic, although nutmeg is more delicate than mace. Both spices are also sold ground.
White pepper comes from ripened berries with the outer husks removed.
Black pepper comes from unripened berries dried until dark greenish-black in color. Black pepper is more subtle than white. Use white or black peppercorns in marinades and pickling, or freshly ground as a seasoning. Both are available ground. Green peppercorns are also unripe berries with a mild, light flavor.