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The balsam poplars — also known as ''Populus'' sect. ''Tacamahaca'' — are a group of about 10 species of poplars, indigenous to North America and eastern Asia, distinguished by the balsam scent of their buds, the whitish undersides of their leaves, and the leaf petiole being round (not flattened) in cross-section. They are large deciduous trees, 30–60 m tall, with leaves with a rounded base, pointed apex, and a whitish waxy coating on the underside of the leaf; this latter distinguishes them from most other poplars. The name is derived from the pleasant balsam smell of the opening buds and leaves in spring, produced by a sticky gum on the buds which also helps protect the buds from insect damage. The balsam poplars are light-demanding trees that require considerable moisture but are tolerant of very cold conditions, occurring further north than other poplars except for the aspens. ==Species== The balsam poplar ''P. balsamifera'' (= ''P. tacamahaca'', ''P. candicans'') is a native of North America, where it grows on alluvial bottomlands in the northeastern United States and Canada. It grows to a height of 30 metres and has yellow-grey bark, thick and furrowed, and coloured blackish at the base of the trunk. The twigs are yellow-brown to brown, the buds covered with a layer of balsam resin. The flowers and fruit are very much like those of the white poplar (''P. alba'') which is a relative of the aspens (''Populus'' sect. ''Populus''). The western balsam poplar, black cottonwood, or California poplar ''P. trichocarpa'' is native to western North America, from Alaska south to northern California. It is the largest species of poplar, recorded to 65 m tall. It is also a very important species in plant biology. It was announced on 15 September 2006 in the journal Science that ''P. trichocarpa'' became the first tree species to have its entire genome sequenced.〔Nature: (First tree joins genome club )〕〔Science:(Seeking the Genome for the Trees )〕 In the mountains of interior western North America, it is replaced by the willow-leaved poplar or narrowleaf cottonwood, ''P. angustifolia''. ''P. trichocarpa'' is sometimes treated within ''P. balsamifera'' as ''P. balsamifera'' ssp. ''trichocarpa.'' Simon's poplar (''P. simonii''), a native of northwestern China,〔(【引用サイトリンク】 work = Flora of China )〕 is frequently planted as a shade tree in northern European cities. It is an attractive ornamental tree with whitish bark, and nearly rhombic, 6–10 cm long leaves which appear on the tree in early spring. Maximowicz' poplar or Japanese poplar (''P. maximowiczii'')〔(【引用サイトリンク】 32. Populus maximowiczii A. Henry )〕 and the Ussuri poplar (''P. ussuriensis'' = ''P. maximowiczii'' var. ''barbinervis''〔(【引用サイトリンク】 33. Populus ussuriensis Komarov )〕) are similar, occurring in northeastern China, Japan, Korea, and eastern Siberia; they have broader leaves. Another similar species is the laurel-leaf poplar (''P. laurifolia'' from Mongolia〔(【引用サイトリンク】 40. Populus laurifolia Ledebour )〕), which differs from its relatives in narrower leaves shaped like a bay laurel leaf. Another putative member of this group is the Korean poplar (''P. koreana''). Whether the northeast Asian Sichuan poplar (''P. szechuanica'') and ''P. tristis'' belong here or with the aspens is not yet resolved. Likewise, the affiliation of ''P. cathayana'' and the Yunnan poplar (''P. yunnanensis'') are in need of further study, though these may well be balsam poplars. There are other species not listed here.〔(【引用サイトリンク】 3. Populus Sect. Tacamahaca Spach )〕 How to classify ''Populus'' into species, at least for Chinese populations, is not yet settled.〔(【引用サイトリンク】 1. Populus Linnaeus )〕 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「Populus sect. Tacamahaca」の詳細全文を読む スポンサード リンク
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