A walnut is the nut of any tree of the genus Juglans (Family Juglandaceae), particularly the Persian or English walnut, Juglans regia. Technically a walnut is the seed of a drupe or drupaceous nut, and thus not a true botanical nut. It is used for food after being processed while green for pickled walnuts or after full ripening for its nutmeat. Nutmeat of the eastern black walnut from the Juglans nigra is less commercially available, as are butternut nutmeats from Juglans cinerea. The walnut is nutrient-dense with protein and essential fatty acids.
Walnuts are rounded, single-seeded stone fruits of the walnut tree commonly used for the meat after fully ripening. Following full ripening, the removal of the husk reveals the wrinkly walnut shell, which is usually commercially found in two segments (three-segment shells can also form). During the ripening process, the husk will become brittle and the shell hardens. The shell encloses the kernel or meat, which is usually made up of two halves separated by a partition. The seed kernels – commonly available as shelled walnuts – are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen, thereby preventing rancidity.
Walnuts are late to grow leaves, typically not until more than halfway through the spring. They secrete chemicals into the soil to prevent competing vegetation from growing. Because of this, flowers or vegetable gardens should not be planted close to them.