Beech (Fagus) is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America. Recent classification systems of the genus recognize ten to thirteen species in two distinct subgenera, Engleriana and Fagus.
The Engleriana subgenus is found only in East Asia, and is notably distinct from the Fagus subgenus in that these beeches are low-branching trees, often made up of several major trunks with yellowish bark. Further differentiating characteristics include the whitish bloom on the underside of the leaves, the visible tertiary leaf veins, and a long, smooth cupule-peduncle. Fagus japonica, Fagus engleriana, and the species F. okamotoi, proposed by the botanist Chung-Fu Shen in 1992, comprise this subgenus. The better known Fagus subgenus beeches are high-branching with tall, stout trunks and smooth silver-grey bark. This group includes Fagus sylvatica, Fagus grandifolia, Fagus crenata, Fagus lucida, Fagus longipetiolata, and Fagus hayatae. The classification of the European beech, Fagus sylvatica is complex, with a variety of different names proposed for different species and subspecies within this region (for example Fagus taurica, Fagus orientalis, and Fagus moesica). Research suggests that beeches in Eurasia differentiated fairly late in evolutionary history, during the Miocene. The populations in this area represent a range of often overlapping morphotypes, though genetic analysis does not clearly support separate species.
Within its family, the Fagaceae, recent research has suggested that Fagus is the evolutionarily most basal group. 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 European beech (Fagus sylvatica) is the most commonly cultivated, although there are few important differences between species aside from detail elements such as leaf shape. 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 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 tannin content, and are called beechnuts or beechmast.
The name of the tree (Latin fagus, whence the species name; cognate with English “beech”) is of Indo-European origin, and played an important role in early debates on the geographical origins of the Indo-European people. Greek φηγός is from the same root, but the word was transferred to the oak tree (e.g. Iliad 16.767) as a result of the absence of beech trees in Greece.