Sitka mountain-ash (western mountain ash)
Rosaceae (Rose family)
Introduction to Vascular Plants
SUBTAXA PRESENT IN BC
Species Information
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
Illustration
If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.
Illustration Source: The Illustrated Flora of British Columbia
Ecology
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 |
||
|
Avg |
Min |
Max |
|
| Elevation
(metres) |
1258 | 0 | 2500 |
| Slope
Gradient (%) |
25 | 0 | 200 |
|
Aspect (degrees) |
250 | 0 | 360 |
| Soil
Moisture Regime (SMR) [0 - very xeric; 4 - mesic; 8 - hydric] |
3 | 0 | 8 |
| Modal
Nutrient Regime
Class |
C | ||
| #
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) | ||
|
Source:
Klinkenberg 2013
|
|||
Habitat and 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.Synonyms
Synonyms and Alternate Names:
Sorbus sitchensis subsp. californica (Greene) Abrams
Taxonomic Keys
1. Plants becoming trees over 5 m tall; leaflets usually more than 13, winter buds covered with long soft-hairy grey hairs; styles 2 or 3...........................S. aucuparia
1. Plants shrubby, usually less than 5 m tall; leaflets rarely as many as 13, winter buds not covered with long soft grey hairs; styles 3 to 5. 2. Winter buds rusty-hairy; calyces smooth on outside; leaflets blunt or rounded at the tip, toothed for not more than 3/4 of their length; styles 4 or 5, fruit red, glaucous...............S. sitchensis 2. Winter buds sticky, sparsely white-hairy; calyces hairy on outside; leaflets sharp-pointed at tip, toothed for most of their length; styles 3 or 4; fruit orange, not glaucous................S. scopulina Source: Illustrated Flora of British Columbia |