E-Flora BC: Electronic Atlas of the Flora of British Columbia

Sorbus sitchensis M. Roem.
Sitka mountain-ash (western mountain ash)
Rosaceae (Rose family)

Introduction to Vascular Plants

© Virginia Skilton  Email the photographer   (Photo ID #9046)

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Distribution of Sorbus sitchensis
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Species Information

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General:
Medium to tall shrub, 1-4 m tall; stems several, erect to spreading, sparingly branched, greyish-red; winter buds and young growth not sticky, somewhat rusty-hairy.
Leaves:
Alternate, deciduous, pinnately compound; leaflets 7 to 11, oblong to oblong-egg-shaped, 2-7 cm long, rounded to blunt at the tip, smooth above, sometimes rusty-hairy below, rather coarsely saw-toothed for not more than 3/4 their length.
Flowers:
Inflorescence a half-rounded, branched cluster of numerous (15 to 80) small flowers, the branches often minutely rusty-hairy; corollas white to cream, the petals 5, oval, 4-6 mm long; calyces mostly smooth, 5-lobed, the lobes triangular; ovaries inferior; stamens 15-20.
Fruits:
Berry-like pomes (like miniature apples), nearly globe-shaped to ellipsoid, 8-10 mm long, red, glaucous, 2- to 5-chambered; seeds 1 or 2 per chamber.
Notes:
Two sympatric varieties occur in BC:

1. Leaflets entire or toothed mostly above midlength................ var. grayi (Wenzig) C.L. Hitchc.

1. Leaflets toothed one-half to three-quarters their length................. var. sitchensis

Source: The Illustrated Flora of British Columbia

Habitat / Range

Mesic to moist open forests, forest edges, streambanks, rockslides, thickets and meadows in the montane to alpine zones; common throughout BC (except NE BC), especially southward; N to AK and YT, E to AB and S to ID, MT and N CA.

Source: The Illustrated Flora of British Columbia

Ecology

Ecological Framework for Sorbus sitchensis

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class

Minimum

Average

Maximum

Elevation (metres) 0 1258 2500
Slope Gradient (%) 0 25 200
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
0 250 360
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
0 3 8
Modal Nutrient Regime
Class
C
Number of field plots
 species was recorded in:
2846
Modal BEC Zone Class
ESSF
All BEC Zones (# of stations/zone) species was recorded in: AT(7), BWBS(19), CDF(4), CMA(1), CWH(190), ESSF(1250), ICH(563), IDF(53), MH(229), MS(146), SBPS(3), SBS(204)

Ecological Indicator Information

A shade-intolerant, montane to subalpine, Western North American deciduous shrub distributed more in the Pacific than the Cordilleran region. Occurs in maritime to submaritime subalpine boreal climates on moderately dry to fresh, nitrogen-poor soils; its occurrence increases with increasing precipitation and elevation, and decreases with continentality. Common but scattered in open-canopy, coniferous forests on water­shedding sites; persists in clearings. Characteristic of Mor humus forms.

SourceIndicator Plants of Coastal British Columbia (Information applies to coastal locations only)

Climate

The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is subalpine boreal & cool mesothermal.

Synonyms and Alternate Names

Sorbus sitchensis subsp. californica (Greene) Abrams

Taxonomic and Nomenclatural Links

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General References