Potatoes
From Tolkien Gateway
Potatoes were root vegetables that were apparently among the staple foods of the Hobbits. How they came to exist in Middle-earth is something of a mystery - in principle, they should not have appeared east of the Great Sea for several thousand years after the War of the Ring. Conceivably, the roots named 'potatoes' in Tolkien's work represent some other related plant, or a crop brought east by the Númenóreans that later became extinct.