Here's why:

* Angiosperms are flowering plants that produce seeds enclosed within a fruit. Peanuts, despite their name, are actually legumes. They develop their seeds within pods, which are a type of fruit.

* Gymnosperms are plants that produce naked seeds, meaning they are not enclosed within a fruit. Examples include conifers like pine trees and fir trees.

So, the peanut's fruit (the pod) clearly distinguishes it as an angiosperm.