Hazels

Hazels have simple, rounded leaves with double-serrate margins. The flowers are produced very early in spring before the leaves, and are monoecious, with single-sex catkins, the male catkins are pale yellow and 5-12 cm long, and the female ones are very small and largely concealed in the buds, with only the bright-red, 1- to 3-mm-long styles visible. The fruits are nuts 1-2.5 cm long and 1-2 cm diameter, surrounded by an involucre (husk) which partly to fully encloses the nut.[3]

The shape and structure of the involucre, and also the growth habit (whether a tree or a suckering shrub), are important in the identification of the different species of hazel.