Answer
Potato is a stem modification (tuber), whereas sweet potato is a root modification (root tuber). Although both structures store food and perform similar functions, they differ in their origin.
This indicates that potato and sweet potato are analogous organs—they have a similar function but different origins. Such structures are a result of convergent evolution, a process where unrelated organisms independently evolve similar traits as an adaptation to similar environments or ecological roles.
Conclusion: The correct terms to describe the evolutionary relationship between sweet potato and potato are Analogy and Convergent Evolution.