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Betula papyrifera
''Betula papyrifera'' (paper birch, also known as white birch〔 and canoe birch〔) is a species of birch native to northern North America. It is the provincial tree of Saskatchewan and the state tree of New Hampshire.〔(【引用サイトリンク】title=Fast New Hampshire Facts )〕
==Description==
It is a medium-sized deciduous tree reaching 60 feet tall (18m), and exceptionally to 130 feet (40m) with a trunk up to 32 inches diameter (0.8m). They live to about 140 years. The bark is white, commonly brightly so, flaking in fine horizontal strips, and often with small black marks and scars. In individuals younger than five years, the bark appears brown with white lenticels, making the tree much harder to distinguish from other trees. The leaves are alternate, ovate, 1-5 in. long and 2-4 in. broad, with a doubly serrate margin. The leaf buds are conical and small. They are green-colored with brown edges. The flowers are wind-pollinated catkins 1.5 in. long growing from the tips of twigs. The fruit matures in the fall. The mature fruit is composed of numerous tiny winged seeds packed between the catkin bracts. They drop between September and spring.
Paper birch handles heat and humidity poorly and may only live 30 years in zones six and up, while trees in colder-climate regions can exceed 50 years and grow to much larger sizes. When stressed, it can succumb to bronze birch borer beetles.
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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