No, truffle is not a root vegetable. In fact, taxonomically speaking, it isn't a vegetable at all. It is a fungus—specifically, a mushroom and the part we eat is the fruiting body, not a root (fungi don't have roots, they have mycelium made up of fungal strings, or hyphae). You may have been led to believe all mushrooms are vegetables because they are included in the vegetable food group by the Food & Drug Administration, due to their nutritional components.