The hazel is a shrub and sometimes small tree of the genus Corylus, sub-family Corylaceae, family Betulaceae. The leaves are roundish-cordate, alternate and shortly petiolate. The bark is reddish-brown and smooth. The plant is monoecious, the male flowers are clustered in pendulous catkins, the female flowers are arranged in erect, short, bud-like spikes with protruding red styles. The fruit is a hard, brown, rounded nut (filbert), enclosed by an irregularly lobed green involucre. Research Hazel