Birch is the name of any tree of the genus Betula (Bé-tu-la), in the family Betulaceae, closely related to the beech/oak family, Fagaceae.

Description

Birch species are generally small to medium-size trees or shrubs, mostly of northern temperate climates. The simple leaves may be toothed or pointed. The fruit is a small samara, although the wings may be obscure in some species. They differ from the alders (Alnus, other genus in the family) in that the female catkins are not woody and disintegrate at maturity, falling apart to release the seeds, unlike the woody cone-like female alder catkins.

The bark of all birches is characteristically marked with long horizontal lenticels, and often separates into thin papery plates, especially upon the Paper Birch. It is practically imperishable, due to the resinous oil which it contains. Its decided color gives the common names Red, White, Black, Silver and Yellow to different species.

The buds form early and are full grown by midsummer, all are lateral, no terminal bud is formed; the branch is prolonged by the upper lateral bud. The wood of all the species is close-grained with satiny texture and capable of taking a fine polish; its fuel value is fair.

The leaves of the different species vary but little. All are alternate, doubly serrate, feather-veined, petiolate, and stipulate. Apparently they often appear in pairs, but these pairs are really borne on spur-like two-leaved lateral branchlets.

Flower and fruit

The flowers are monoecious, opening with or before the leaves and borne on three-flowered clusters in the axils of the scales of drooping or erect aments. Staminate aments are pendulous, clustered or solitary in the axils of the last leaves of the branch of the year or near the ends of the short lateral branchlets of the year. They form in early autumn and remain rigid during the winter. The scales of the staminate aments when mature are broadly ovate, rounded, yellow or orange color below the middle, dark chestnut brown at apex. Each scale bears two bractlets and three sterile flowers, each flower consisting of a sessile, membranaceous, usually two-lobed, calyx. Each calyx bears four short filaments with one-celled anthers or strictly, two filaments divided into two branches, each bearing a half-anther. Anther cells open longitudinally. The pistillate aments (catkins) are erect or pendulous, solitary; terminal on the two-leaved lateral spur-like branchlets of the year. The pistillate scales are oblong-ovate, three-lobed, pale yellow green often tinged with red, becoming brown at maturity. These scales bear two or three fertile flowers, each flower consisting of a naked ovary. The ovary is compressed, two-celled, and crowned with two slender styles; the ovule is solitary.