Corylus

Corylus is a genus of deciduous shrubs and small trees in the birch family Betulaceae, native to temperate regions of the Northern Hemisphere. The genus comprises about 15 species, with Corylus avellana (the common hazel) and Corylus colurna (Turkish hazel) among the best known for nut production. Hazelnuts, or filberts, have been cultivated for centuries for eating, oil, and culinary uses, and the plants are also valued as ornamental hedges and in agroforestry systems.

Description: Corylus species are typically multi-stemmed in form, with rounded to upright crowns. Leaves are alternately arranged, simple, ovate to round, and doubly serrate, often hairy on the undersides. Male catkins appear in late winter as pendulous clusters, while female flowers are inconspicuous. The edible fruits are nuts enclosed by a scaly involucre (cupule) that partly covers the nut.

Major species and distribution: The most widely grown is Corylus avellana, native to Europe and western Asia. Other well-known species include Corylus americana in eastern North America and Corylus heterophylla in Asia. Corylus colurna is a large, drought-tolerant tree native to the Balkans and western Asia and is widely used as rootstock and for ornamental plantings.

Cultivation and uses: Corylus nut crops are cultivated commercially in temperate regions for fresh and processed nuts, chocolate and confectionery products, and oil. Plants prefer well-drained soils, moderate moisture, and a climate with sufficient chilling hours. Propagation is by seed or vegetative methods such as cuttings and grafting; C. colurna is often used as rootstock for improved vigor and disease resistance.

Pests and diseases: Hazelnuts are subject to pests and diseases including eastern filbert blight (Anisogramma anamola), leaf diseases, and various insect pests such as hazelnut weevils. Integrated management and resistant cultivars are important for commercial production.