Corylus
The hazelnut is the  nut of the hazel and therefore includes any of the nuts deriving from species of the genus Corylus, especially the nuts of the species Corylus avellana. It also is known as cobnut or filbert nut according to species. A cob is roughly spherical to oval, about 15â25 mm long and 10â15 mm in diameter, with an outer fibrous husk surrounding a smooth shell and a filbert is more elongated, being about twice as long as its diameter. The nut falls out of the husk when ripe, about seven to eight months after pollination. The kernel of the seed is edible and used raw or roasted, or ground into a paste. The seed has a thin, dark brown skin, which sometimes is removed before cooking.