Northern Ontario Plant Database

Plant Description

Sorbus decora (Sarg.) C.K.Schneid.

En: northern mountainash, showy mountainash
Fr: sorbier de montagne, sorbier plaisant

Rosaceae (Rose Family)

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General: A tall, open, deciduous shrub or small tree, to 10 m tall.

Stems/twigs: Bark grayish-brown, smooth; twigs are stout, smooth (glabrous), and dark reddish-brown. Both terminal and lateral buds are present; the large, scaly buds are alternate, lanceolate, dark reddish-brown, and sticky (resinous); buds are often curved slightly at the tip. Leaf scars are narrow, broadly U- or V-shaped, and have 5 bundle trace scars.

Leaves: Alternate, pinnately compound, with 13—17 leaflets, and petiolate. The terminal leaflet is obovate, with a long stalk (petiolule), while lateral leaflets are oblong to lanceolate-oblong and short-stalked; the rachis is reddish-green to deep red. Leaflet blades are 3—8 cm long by 1.5—3 cm wide (2-3 times as long as broad); bluish-green to dark green and smooth (glabrous) above, much paler and smooth to slightly hairy beneath; bases are blunt, rounded, or slightly oblique, i.e., the blade is longer on the lower side of the midrib; leaflets narrow abruptly to a short, pointed tip (acuminate); margins are sharply toothed (serrate) or double-toothed (double-serrate). Leaves turn yellow to red-orange in fall.

Flowers: Bisexual, white, numerous, in a terminal, branched, flat to dome-shaped inflorescence (compound cyme), 6—16 cm across. Flowers are about 1 cm across and have a hypanthium with 5 triangular calyx lobes, 5 rounded white petals, about 20 stamens, and a pistil with an inferior ovary of 2—5 carpels and styles. Flowers bloom in late spring to early summer (June).

Fruit: A cluster of red-orange, berry-like fruit (pomes), each 8—12 mm across; mature fruiting stalks (pedicels) are red. Fruits mature in late summer.

Habitat and Range: Moist to dry woods, rocky shores, thickets, and slopes. Showy mountain-ash is native to boreal northeastern North America; its range extends from Newfoundland and Labrador west to Saskatchewan. In Ontario, it occurs mainly between 45° N and 54° N (Soper & Heimburger 1982).

Similar Species: American mountain ash (Sorbus americana Marshall), is similar to showy mountain ash, but has narrower leaflets with longer, gradually tapering tips and smaller fruit, 5—6 mm in diameter. The leaflets of mature American mountain ash leaves are 3.5—5 times longer than wide, compared to 2—3 times longer than wide in showy mountain ash.

Sumac (Rhus spp.) leaves are also pinnately compound, but their leaflets are sessile, not stalked. The stems and leaf rachises of Rhus typhina L. (staghorn sumac) are hairy, while those of Rhus glabra L. (smooth sumac) are glabrous to glaucous. Sumac twigs are also very stout, but their low, dome-shaped buds are covered in golden-brown hairs and the C-shaped leaf scars nearly encircle the buds.

Common elderberry (Sambucus canadensis L.) has flat-topped inflorescences similar to those of Sorbus, but the elderberry flowers are much smaller, more numerous, and have only 5 stamens. The fruits of common elderberry are small purplish-black drupes.