The American mountain ash and related species (most often the European mountain ash, Sorbus aucuparia) are also referred to as rowan trees.
Sorbus americana
Description
Sorbus americana is a relatively small tree, reaching 12 metres (40 ft) in height. The American mountain-ash attains its largest specimens on the northern shores of Lake Huron and Lake Superior.
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, 6 to 10 inches (15 to 25 cm) 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; 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.
Distribution
Native to eastern North America;
Eastern Canada – New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec
Northeastern United States – Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Vermont
North-Central United States – Illinois [n. (Ogle Co.)], Michigan, Minnesota, Wisconsin. Listed as endangered by the State of Illinois
The berries of American mountain-ash are eaten by numerous species of birds and small mammals, including ruffed grouse, ptarmigans, sharp-tailed grouse, blue grouse, American robins, other thrushes, waxwings, jays, 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.
