The European beech(Fagus sylvatica) is the most commonly cultivated, although there are few important differences between species aside from detail elements such as leaf–10 cm broad. Beeches are moecious, bearing both male and female flowers on the same plant. The small flowers are unisexual, the female flowers borne in pairs, the male flowers wind-pollinating catkins. They are produced in spring shortly after the new leaves appear. The bark is smooth and light grey. The fruitis a small, sharply three–angled nut 10–15 mm long, borne singly or in pairs in soft-spined husks 1.5–2.5 cm long, known as cupules. The husk can have a variety of spine- to scale-like appendages, the character of which is, in addition to leaf shape, one of the primary ways beeches are differentiated. The nuts are edible, though bitter (though not nearly as bitter as acorns) with a high tannincontent, and are called beechnuts or beechmast.