Beech (Fagus) is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America. F. sylvatica is the most commonly cultivated, although there are few important differences between species aside from detail elements such as leaf shape. Beeches are large trees that may exceed 35 meters in height and 1.5 metres in diameter at breast height.
The southern beeches (Nothofagus genus) previously thought closely related to beeches, are now treated as members of a separate family, Nothofagaceae. They are found in Australia, New Zealand, New Guinea, New Caledonia, Argentina and Chile (principally Patagonia and Tierra del Fuego).
The leaves of beech trees are entire or sparsely toothed, from 5–15 cm long and 4–10 cm broad. Beeches are monoecious, 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 fruit is 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 nuts are edible, though bitter (though not nearly as bitter as acorns) with a high tannin content, and are called beechnuts or beechmast. They often fail to fill in, especially on solitary trees.