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Many plants in the Betula genus are hardy, short-lived, deciduous birch trees. The arctic birch, or B. nana, which is native in Arctic areas, is a ground-hugging shrub, but most are erect trees. There are about 60 species in the Betula genus, which belongs to the Betulaceae family. At least 10 species grow naturally in regions of the US and Canada, and the remaining species are native to regions in Europe; parts of Asia, including the islands of Japan and Korea; and the Himalayas. Although people associate white, papery bark with birch trees, many species do not have white bark.
One popular birch is the paper or canoe birch, scientifically named B. papyifera. With proper growing conditions, this birch may grow 70 feet (about 21 m) or higher. Like its cousin, the European white birch, or B. pendula, its white bark peels easily. The paper birch is native to the northern US and most of Canada and Alaska. Landscapers and gardeners introduced the European white birch into many regions of North America.
Bark color may range from orange-brown, like B. nigra and B. albosinensis bark, to brownish-black, similar to B. schmidtii bark. The B. nigra, commonly called the red or river birch, has bark that often turns to dark brown or black with maturity. Some species and their varieties or cultivars have reddish gray, pinkish white, or reddish brown bark. The bark of many species darkens with age.
Another birch trait is that frequently the bark peels into long horizontal strips. Most Betula species have waterproof bark, which is why many American and Canadian natives used it for canoes, cooking containers, and roofing material. With traditional techniques, the canoe builders peeled the bark from large trees in one, entire sheet. In modern times, canoe builders make canoes for tourists and decoration. They did not use the birch wood in canoes because it is too dense and heavy to float.
Birch trees have catkins as part of the reproductive system. A catkin is a form of inflorescence, meaning several flowers are arranged on a single axis. The birch catkins often are pendent and consist of scale-like bracts and tiny flowers. Typically, in Betula plants, these flowers are petal-less and arranged in a spike. In most birches, when the catkin matures, it disintegrates and spreads its seeds.
Generally, the catkins differ in size, depending upon the sex. The male catkins, or staminate strobili, range from 1 inch to 4 inches (about 2.5 to 10 cm) long, whereas the female ones, or pistillate strobili, grow up to 1.5 inches (about 2 cm) long. Some Betula trees have tassel-like, pendent catkins, and others have rounder, erect ones that resemble miniaturized pinecones. Typically, the staminate catkins develop in the previous season.
In landscaping, birches are frequently specimen plants. Foresters plant birches for lumber to make veneer, furniture, and pulp. Typically, it yields very strong, close-grained wood, and wagon builders used it for wheel hubs. In parts of Europe, the European white birch is an important commercial product.
Medicinally, parts of most Betula plants are emetic and cathartic. Native Americans used a bark decoction to purify the blood. Some Betula trees are a source of oil of wintergreen, which people mostly use as a flavoring, but it does have a few medicinal qualities.
The inner bark of the yellow birch, or B. alleghaniensis, is edible. In the past, Native Americans cooked it or used a dried and powdered form in a process similar to bread making. Usually, they ate it only in times of famine. Some people harvest and process the sap in a method that is comparable to maple sap harvesting. A few brewers make a beer from the sap, and other people drink it unfermented.
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