An acorn is the nut of an oak tree, usually about the size of a large marble, with a smooth shell and a distinctive cap that looks like a little beret. If you've ever walked under oak trees in fall, you've probably seen hundreds of acorns scattered on the ground or heard them plinking off car roofs.

Inside each acorn is a seed that can grow into a mighty oak tree, which is why people sometimes say “great oaks from little acorns grow” when talking about how something small can become something magnificent. A tiny acorn that weighs less than an ounce contains everything needed to become a tree that might live 300 years and tower 100 feet tall.

Many animals depend on acorns for food. Squirrels famously gather and bury thousands of acorns each fall, forgetting where they hid many of them. Those forgotten acorns often sprout into new oak trees, which means squirrels accidentally plant forests while trying to store their winter food. Deer, wild turkeys, bears, and even woodpeckers also eat acorns. Some Native American peoples learned to process acorns by soaking them to remove their bitter taste, then grinding them into nutritious flour for bread and soup.