acorn

An acorn is the nut of oak trees, belonging to the genus Quercus. Each acorn is a single seed encased in a hard shell, usually borne in a cup-like involucre called a cupule. Acorns vary in size from about 1 cm to more than 4 cm long, depending on the species.

Oak species native to temperate regions of the Northern Hemisphere produce acorns once or twice a year, with fruit development taking several months. In autumn the nuts mature and fall to the ground; the cupule often remains attached to the shell. Acorns may remain on the ground to overwinter before germination, depending on local climate and species.

Acorns contain tannins that can give a bitter taste and can be toxic in large amounts if eaten raw. They are often leached in water to remove tannins, after which they can be dried, ground into flour or meal, and used for bread, porridge, or other foods. In some cultures acorns are an important traditional staple, particularly in regions where oak forests are common.

Ecologically, acorns are a major food resource for wildlife and play a key role in oak forest dynamics. They are dispersed and cached by animals such as squirrels, jays, and mice; many cached seeds are not retrieved and eventually germinate. Germination typically occurs in spring after a period of cold stratification.

Humans have utilized acorns as a food source for millennia in various cultures, and they continue to be recognized for their ecological importance within oak ecosystems. The acorn also appears in cultural symbolism as a sign of potential and growth.