Acorn

The acorn is the nut of the oaks and their close relatives (genera Quercus, Notholithocarpus and Lithocarpus, in the family Fagaceae); alternatively known as glans. It usually contains a seedling surrounded by two cotyledons (seedling leaves), enclosed in a tough shell known as the pericarp, and borne in a cup-shaped cupule. Acorns are 1–6 cm (1⁄2–2+1⁄2 in) long and 0.8–4 cm (3⁄8–1+5⁄8 in) on the fat side. Acorns take between 5 and 24 months (depending on the species) to mature; see the list of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.