Birch is a tree or shrub of the genus
Betula (Bé-tu-la), in the family Betulaceae,
closely related to the beech/oak family, Fagaceae.
The Betula genus contains 30–60 known taxa.
It is widespread on the Northern Hemisphere, across
a variety of boreal, mountainous and temperate climates.
The common name birch is derived from an old Germanic
root, birka, with the Proto-Indo-European root,
"white, bright; to shine." The Proto-Germanic
rune berkanan is named after the birch. The botanic
name Betula is from Latin.
Birch species are generally small to medium-size
trees or shrubs, mostly of temperate climates. The
simple leaves are alternate, doubly serrate, feather-veined,
petiolate, and stipulate. They often appear in pairs,
but these pairs are really borne on spur-like two-leaved
lateral branchlets. 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 gray, white, black, silver
and yellow birch 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.