Which one is not correctly matched?

Solution(By Examveda Team)

Ginger is a rhizome that grows at, or just under, the surface of the soil. The rhizome sprouts green foliage upward, to about three feet above the ground, while producing roots from its undersurface.
Garlic is a bulbous herb - which means that it grows with individual pieces packed together. Each of these lobes is called a clove of garlic.
Potatoes are stem tubers - enlarged stolons thicken to develop into storage organs. The tuber has all the parts of a normal stem, including nodes and internodes.
Sweetpotato is the storage root of the plant; an enlarged lateral root. It is not a type of stolon. Thus it is wrongly matched.