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''Betula glandulosa'', American Dwarf Birch, also known as Resin Birch or Shrub Birch, is a species of birch native to North America, occurring in arctic and cool temperate areas from Alaska east to Newfoundland and southern Greenland, and south at high altitudes to northern California and Colorado in the west, and locally south to northern New York in the east. In the Arctic it occurs down to sea level, while in the south of the range, it grows as high as 3400 m altitude. American Dwarf Birch is a multi-stemmed shrub typically growing to 1–3 m tall, often forming dense thickets. The trunks are slender, rarely over 5–10 cm diameter, with smooth, dark brown bark. The leaves are nearly circular to oval, 0.5–3 cm long and 1.2.5 cm broad, with a toothed margin. The fruiting catkins are erect, 1-2.5 cm long and 5–12 mm broad. It is closely related to the Dwarf Birch (''Betula nana''), and is sometimes treated as a subspecies of it, as ''B. nana'' subsp. ''glandulosa''. It is distinguished from typical ''B. nana'' by the presence of glandular warts on the shoots and longer leaf petioles. Hybrids with several other birches occur. ==References== *(Flora of North America: ''Betula glandulosa'' ), (RangeMap ) *Hunt, D. (1993). ''Betula. Proceedings of the IDS Betula Symposium 2–4 October 1992''. International Dendrology Society. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Betula glandulosa」の詳細全文を読む スポンサード リンク
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