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The tree species ''Sorbus americana'' (syn. ''Pyrus americana'') is commonly known as the American mountain ash.〔http://plants.usda.gov/java/charProfile?symbol=SOAM3 USDA Natural Resources Conservation Service〕 It is a deciduous perennial tree, native to eastern North America.〔 The American mountain ash and related species (most often the European mountain ash, ''Sorbus aucuparia'') are also referred to as rowan trees. == Description == ''Sorbus americana'' is a relatively small tree, reaching in height.〔 The American mountain-ash attains its largest specimens on the northern shores of Lake Huron and Lake Superior. It resembles the European mountain-ash, ''Sorbus aucuparia''. * Bark: Light gray, smooth, surface scaly. Branchlets downy at first, later become smooth, brown tinged with red, lenticular, finally they become darker and the papery outer layer becomes easily separable. * Wood: Pale brown; light, soft, close-grained but weak. Sp. gr., 0.5451; weight of cu. ft., 33.97 lbs. * Winter buds: Dark red, acute, one-fourth to three-quarters of an inch long. Inner scales are very tomentose and enlarge with the growing shoot. * Leaves: (see Leaf shape for explanation of terms) Alternate, compound, odd-pinnate, six to ten inches long, with slender, grooved, dark green or red petiole. Leaflets thirteen to seventeen, lanceolate or long oval, two to three inches long, one-half to two-thirds broad, unequally wedge-shaped or rounded at base, serrate, acuminate, sessile, the terminal one sometimes borne on a stalk half an inch long, feather-veined, midrib prominent beneath, grooved above. They come out of the bud downy, conduplicate; when full grown are smooth, dark yellow green above and paler beneath. In autumn they turn a clear yellow. Stipules leaf-like, caducous. * Flowers: May, June, after the leaves are full grown. Perfect, white, one-eighth of an inch across, borne in flat compound cymes three or four inches across. Bracts and bractlets acute, minute, caducous. * Calyx: Urn-shaped, hairy, five-lobed; lobes, short, acute, imbricate in bud. * Corolla: Petals five, creamy white, orbicular, contracted into short claws, inserted on calyx, imbricate in bud. * Stamens: Twenty to thirty, inserted on calyx tube; filaments thread-like; anthers introrse, two-celled; cells opening longitudinally. * Pistil: Two to three carpels inserted in the bottom of the calyx tube and united into an inferior ovary. Styles two to three; stigmas capitate; ovules two in each cell. * Fruit: Berry-like pome, globular, one-quarter of an inch across, bright red, borne in cymous clusters. Ripens in October and remains on the tree all winter. Flesh thin and sour, charged with malic acid; seeds light brown, oblong, compressed; cotyledons fleshy.〔 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「Sorbus americana」の詳細全文を読む スポンサード リンク
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