The tree species Sorbus americana is commonly known as the American mountain-ash. It is a deciduous perennial tree, native to eastern North America. The American mountain-ash and related species 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. Specific gravity, 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: Alternate, compound, odd-pinnate, long, with slender, grooved, dark green or red petiole. Leaflets 13 to 17, 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; stigmascapitate; 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.
The berries of American mountain-ash are eaten by numerous species of birds, including ruffed grouse, ptarmigans, sharp-tailed grouse, blue grouse, American robins, other thrushes, waxwings, jays, and small mammals, such as squirrels and rodents. American mountain-ash is a preferred browse for moose and white-tailed deer. Moose will eat foliage, twigs, and bark. Up to 80 percent of American mountain-ash stems were browsed by moose in control plots adjacent to exclosures on Isle Royale. Fishers, martens, snowshoe hares, and ruffed grouse also browse American mountain-ash.
Cultivation
Sorbus americana is cultivated as an ornamental tree, for use in gardens and parks. It prefers a rich moist soil and the borders of swamps, but will flourish on rocky hillsides. A cultivar is the red cascade mountain-ash, or Sorbus americana 'Dwarfcrown'. It is planted in gardens, and as a street tree.
