Mushroom kingdom. Fungus kingdom. Fungi kingdom. Mushrooms, fungi! What's the difference? The words fungus and mushroom or fungi and mushrooms are often freely substituted for one another. Fungi kingdom is mushroom kingdom and likewise mushroom kingdom is fungi kingdom. Common usage often doesn't really distinguish much between the two terms mushroom and fungi, but there is a difference. Properly speaking a mushroom is a fruitbody of a fungus. When you inspect a wild mushroom or a troop of wild mushrooms, you may never see the underlying fungus at all. It may be hidden under the soil or concealed out of sight inside the bark of a tree or stump from which the mushrooms spring forth. Without the fungus, there would be no mushrooms at all. The fungus multiplies when the mushroom releases spores which land in a nourishing spot and germinate.