Beech

Beech (genus Fagus) is a genus of deciduous trees in the family Fagaceae, native to subtropical (accessory forest element) and temperate (as dominant element of mesophytic forests) Eurasia and North America. There are 14 accepted species in two distinct subgenera, Englerianae Denk & G.W.Grimm and Fagus. The subgenus Englerianae is found only in East Asia, distinctive for its low branches, often made up of several major trunks with yellowish bark. The better known species of subgenus Fagus are native to Europe, western and eastern Asia and eastern North America.

The European beech Fagus sylvatica is the most commonly cultivated species, with several ornamental varieties, and forest trees yielding a timber used for furniture, flooring and construction, plywood, and household items. The timber can be used to build homes. Beechwood makes excellent firewood. Slats of washed beech wood are spread around the bottom of fermentation tanks for some beers. Beech logs are burned to dry the malt used in some German smoked beers. Beech is also used to smoke Westphalian ham, andouille sausage, and some cheeses.

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. The fruit is a three-angled nut, with two in a spiny dehiscent cupule. The bark is smooth. The leaves have a central vein with side-veins parallel to each other and ending in a tooth on the thin leaf-blade. The tree is deciduous, dropping its leaves in autumn.

Numerous species have been named globally from the fossil record spanning from the Cretaceous to the Pleistocene. Some fossil species formerly placed in Fagus have been moved to other genera, namely Alnus, Castanea, Fagopsis, Fagoxylon, Fagus-pollenites, Juglans, Nothofagaphyllites, Nothofagus, and Trigonobalanus.

Fagus is the first diverging lineage in the evolution of the Fagaceae family, which includes oaks and chestnuts. The oldest fossils that can be assigned to the beech lineage are 81–82 million years old pollen from the Late Cretaceous of Wyoming, United States.

The first representatives of the modern-day genus were likely already present in the Paleocene of Arctic North America (western Greenland) and quickly radiated across the high latitudes of the Northern Hemisphere, with a first diversity peak in the Miocene of northeastern Asia. The contemporary species are the product of past, repeated reticulate evolutionary processes (outbreeding, introgression, hybridization). As far as studied, heterozygosity and intragenomic variation are common in beech species, and their chloroplast genomes are nonspecific with the exception of the Western Eurasian and North American species.

A cladogram of 11 extant beech species is shown below. The subgenera Engleriana and Fagus diverged from each other in the Early Oligocene era, 32.1 to 33.4 million years ago.

The most recent classification system of the genus recognizes 14 species in two distinct subgenera, subgenus Englerianae and Fagus. Beech species can be diagnosed by phenotypical and/or genotypical traits. Species of subgenus Engleriana are found only in East Asia, and are notably distinct from species of subgenus Fagus in that these beeches are low-branching trees, often made up of several major trunks with yellowish bark and a substantially different nucleome (nuclear DNA), especially in noncoding, highly variable gene regions such as the spacers of the nuclear-encoded ribosomal RNA genes (ribosomal DNA). Further differentiating characteristics include the whitish bloom on the underside of the leaves, the visible tertiary leaf veins, and a long, smooth cupule-peduncle. Originally proposed but not formalized by botanist Chung-Fu Shen in 1992, this group comprised two Japanese species, F. japonica and F. okamotoi, and one Chinese species, F. engleriana. While the status of F. okamotoi remains uncertain, the most recent systematic treatment based on morphological and genetic data confirmed a third species, F. multinervis, endemic to Ulleungdo, a South Korean island in the Sea of Japan. The beeches of Ulleungdo have been traditionally treated as a subspecies of F. engleriana, to which they are phenotypically identical, or as a variety of F. japonica. The differ from their siblings by their unique nuclear and plastid genotypes.