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Betula nigra
''Betula nigra'' (black birch, river birch, water birch) is a species of birch native to the Eastern United States from New Hampshire west to southern Minnesota, and south to northern Florida and west to Texas. It is one of the few heat-tolerant birches in a family of mostly cold-weather trees which do not thrive in USDA Zone 6 and up. ''B. nigra'' commonly occurs in flood plains and/or swamps.〔Flora of North America: (''Betula nigra'' )〕
It is a deciduous tree growing to with a trunk in diameter, often with multiple trunks. The bark is variable, usually dark gray-brown to pinkish-brown and scaly, but in some individuals, smooth and creamy pinkish-white, exfoliating in curly papery sheets. The twigs are glabrous or thinly hairy. The leaves are alternate, ovate, long and broad, with a serrated margin and five to twelve pairs of veins. The flowers are wind-pollinated catkins long, the male catkins pendulous, the female catkins erect. The fruit is unusual among birches in maturing in late spring; it is composed of numerous tiny winged seeds packed between the catkin bracts.〔〔USDA Silvics Manual: (''Betula nigra'' )〕
==Cultivation and uses==
While its native habitat is wet ground, it will grow on higher land, and its bark is quite distinctive, making it a favored ornamental tree for landscape use. A number of cultivars with much whiter bark than the normal wild type have been selected for garden planting, including 'Heritage' and 'Dura Heat'; these are notable as the only white-barked birches resistant to the bronze birch borer ''Agrilus anxius'' in warm areas of the southeastern United States of America.〔Harlow, W. M., & Harrar, E. S. (1969). ''Textbook Of Dendrology'' 5th ed., LOC# 68-17188〕
Native Americans used the boiled sap as a sweetener similar to maple syrup, and the inner bark as a survival food. It is usually too contorted and knotty to be of value as a timber tree.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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