birch

Birch is the name of any tree of the genus Betula, in the family Betulaceae, closely related to the beech/oak family, Fagaceae. These are generally small to medium-size trees or shrubs, mostly of northern temperate climates. The simple leaves may be toothed or lobed. The fruit is a small samara, although the wings may be obscure in some species. They differ from the alders (Alnus, the 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 common name birch is derived from an old Germanic root similar to birka. The botanic name Betula is from the original Latin.

Birch is used as a food plant by the larvae of a large number of Lepidoptera species, see List of Lepidoptera which feed on Birches.

Species

See also: Betula classification

Birches of North America include

• Betula allegheniensis - Yellow Birch (B. lutea)
• Betula cordifolia - Mountain Paper Birch
• Betula glandulosa - American Dwarf Birch
• Betula lenta - Sweet Birch, Cherry Birch, or Black Birch
  • Betula lenta subsp. uber - Virginia Round-Leaf Birch (endemic, Cressy Creek, Smyth County, Virginia)
• Betula michauxii - Newfoundland Dwarf Birch
• Betula nana - Dwarf Birch or Bog Birch (also in northern Europe and Asia)
• Betula neoalaskana - Alaska Birch or Yukon Birch
• Betula nigra - River Birch or Black Birch
• Betula occidentalis - Water Birch or Red Birch (B. fontinalis)
• Betula papyrifera - Paper Birch, Canoe Birch or American White Birch
• Betula populifolia - Gray Birch
• Betula pumila - Swamp Birch

Birches of Europe and Asia include

• Betula albosinensis - Chinese Red Birch
  • Betula albosinensis var. septentrionalis - North Chinese Red Birch
• Betula alnoides - Alder-leaf Birch
• Betula austrosinensis - South China Birch
• Betula chinensis - Chinese Dwarf Birch
• Betula ermanii - Erman's Birch
• Betula grossa - Japanese Cherry Birch
• Betula jacquemontii (Betula utilis subsp. jacquemontii) - White-barked Himalayan Birch
• Betula mandschurica - Manchurian Birch
  • Betula mandschurica var. japonica - Japanese Birch
• Betula maximowiczii - Monarch Birch
• Betula medwediewii - Caucasian Birch
• Betula nana - Dwarf Birch (also in northern North America)
• Betula pendula - Silver Birch
• Betula platyphylla (Betula pendula var. platyphylla) - Siberian Silver Birch
• Betula pubescens - White Birch, European White Birch or Downy Birch (also in northern Asia)
  • Betula pubescens subsp. tortuosa - Arctic White Birch (subarctic Eurasia, Greenland)
• Betula szechuanica (Betula pendula var. szechuanica) - Sichuan Birch
• Betula utilis - Himalayan Birch

Note: many American texts have B. pendula and B. pubescens confused, though they are distinct species with different chromosome numbers

Uses

Birches are versatile trees. The sap, bark, leaves, wood, twigs, and roots are used for food, construction materials, medicinal treatments, lubricants, and other practical applications.

In northern latitudes birch is however considered to be the most important allergenic tree pollen, with an estimated 15-20% of hay fever sufferers sensitive to birch pollen grains.

Extracts of birch are used for flavoring or leather oil, and in cosmetics such as soap or shampoo. In the past, commercial oil of wintergreen (methyl salicylate) was made from the Sweet Birch (Betula lenta). Birch tar, extracted from birch bark, was used as a lubricant and for medicinal purposes. Xylitol can also be extracted from birch, a sugar alcohol artificial sweetener, which has shown effectiveness in preventing, and in some cases repairing, tooth decay.

In Belarus, Russia, the Baltic States, Finland, and parts of northern China, birch sap is drunk as a refreshing beverage, and is believed to have tonic qualities. It is watery and pale green in color, with a slightly sweet flavor, and is bottled commercially. Birch sap may also made into kvass. The sap of particular birch species may also be rendered into birch syrup, vinegar, beer, soft drinks, and other foods. In contrast to maple syrup, birch syrup is very difficult to produce, making it more expensive than other food syrups. It is also considerably less sweet than maple syrup and the sap for syrup production is not available until a month later than maple's. The syrup is made mainly in Alaska (from Alaska Birch) and Russia (from several species), and more rarely elsewhere.

Silver Birch (Betula pendula) is Finland's national tree. Occasionally one uses leafy, fragrant twigs of silver birch to gently beat oneself in a sauna. The twigs are called vihta or vasta. This has a relaxing effect on the muscles.

Birch is used as firewood due to its high calorific value per unit weight and unit volume.

Birch leaves are used to make a diuretic tea and to make extracts for dyes and cosmetics.

Birch twigs were bound in a bundle, also called birch, to be used for birching, a form of corporal punishment.

Many of the First Nations of North America prized the birch for its bark, which due to its light weight, flexibility, and the ease with which it could be stripped from fallen trees, was often used for the construction of strong, waterproof but lightweight canoes, bowls, and tipis. The bark is high in betulin and betulinic acid, phytochemicals which have potential as pharmaceuticals, and other chemicals which show promise as industrial lubricants.

Birch bark is also used to start fires. The bark will burn very well, even when wet, because of the oils present in the bark; with care, it can be split into very thin sheets that will ignite from even the smallest of sparks.

Birches also have spiritual importance in several religions, both modern and historical.

Birch wood is also used to make drums. They produce a low-resonance that is ideal for studio recordings.

The Proto-Germanic rune berkanan is named after the birch.

External links

• Flora of North America: Betula
• Flora of China: Betula
• The Monday Garden: Birches
• Virtual tour of syrup-producing facility