British Wildlife Wiki

Corylus maxima, the Filbert, is a species of hazel native to southeastern Europe and southwestern Asia, from the Balkans to Ordu in Turkey.

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 1–3 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.