The
acorn is the
nut of the
oak tree and its close relatives, in the family
Fagaceae. Acorns usually contain a
seedling surrounded by two
cotyledons (seedling leaves), enclosed in a tough
shell known as the pericarp, and borne in a cup-shaped
cupule. This acorn of the species
Quercus robur (the pedunculate oak), with a length of 25 millimetres (1 inch), was photographed in
Keila, Estonia.
Photograph credit: Ivar Leidus