Filbert — The filbert, or hazelnut or Corylus maxima, is the fruit of plants belonging to the genus Corylus of the birch family, Betulaceae. Of the 10 major species, the most widely grown are the European filbert (C. avellana), the American filbert (C. americana), the Turkish filbert (C. colurna), and the beaked filbert (C. cornuta). Filberts are deciduous shrubs or small trees (although some varieties may reach heights of 18 m/60 ft) native to the temperate zone. Native varieties grow wild throughout America but are cultivated only in areas that do not have late spring frosts, since the flowers, which open in mild winter and early spring weather, are vulnerable to frost-kill.
The Filbert or Corylus maxima is a species of hazel native to southeastern Europe and southwestern Asia. It is a deciduous shrub 6–10 m tall, with stems up to 20 cm thick. The leaves are rounded, 5–12 cm long by 4–10 cm broad, with a coarsely double-serrated margin. The flowers are wind-pollinated catkins produced in late winter; the male (pollen) catkins are pale yellow, 5–10 cm long, while the female catkins are bright red and only 2–3 mm long. The fruit is a nut produced in clusters of 1–5 together; each nut is 1.5–2.5 cm long, fully enclosed in a 3–5 cm long, tubular involucre (husk).
The Filbert is similar to the related Common Hazel (C. avellana), differing in having the nut more fully enclosed by the tubular involucre. This feature is shared by the Beaked Hazel (C. cornuta) of North America, and the Asian Beaked Hazel (C. sieboldiana) of eastern Asia.
Most filberts require more than one variety for pollination. They grow in a wide range of soils and are propagated by seed, layering, or grafting. Commercial production of filberts in the United States is centered in Oregon and Washington. The major filbert-exporting countries are Turkey, Italy, and Spain.