Peanuts grow underground, which is why they are legumes rather than tree nuts.

The longer version

After a peanut flower is pollinated above ground, the stalk bearing the fertilized ovary elongates, bends downward, and pushes the developing pod into the soil, where it matures out of sight. That unusual habit is why the plant is described as geocarpic.

The edible part is a seed inside a pod that splits along a seam, which places peanuts in the legume family alongside beans and lentils rather than among tree nuts such as walnuts or almonds. Legumes also host nitrogen-fixing bacteria in their roots, so the crop is often rotated to return nitrogen to the soil. The buried habit also protects the developing seed.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.