A tuber is a thick, rounded part of an underground stem or root that plants use to store food and energy, usually starch. Potatoes are the most famous tubers: those brown lumps aren't actually roots but swollen stems growing beneath the soil. When you plant a potato, you're really planting a chunk of stored energy that will sprout into a new plant.

Many plants develop tubers as a survival strategy. During the growing season, the plant packs extra nutrients underground. Then, when conditions get harsh (like during winter or drought), the plant can draw on those reserves, or the tuber can sprout into an entirely new plant when conditions improve. It's like a natural pantry built right into the plant's body.

Besides potatoes, other common tubers include yams, Jerusalem artichokes, and cassava (a major food source in tropical regions). Sweet potatoes are technically not tubers but tuberous roots, which work similarly but form from actual roots rather than stems.

People have cultivated tubers for thousands of years because they're nutritious and store well.