Sorbus torminalis
Sorbus scopulina
checkertree, wild service tree
Cascade mountain-ash, Greene's Mountain ash, mountain ash, Rocky Mountain ash, Rocky Mountain Mountain ash, Rocky Mountain or Cascade Mountain ash, Rocky Mountain or Cascade or Greene's Mountain Ashe, western mountain-ash
1;
bark gray;
winter buds green to brown, ovoid to ovoid-oblong, 5–10 mm, scales dark-margined, shiny, glutinous, glabrous, ciliate, or villous.
1–8;
bark gray, sometimes yellowish or reddish purple, or grayish red;
winter buds olive brown to red-brown, conic, 8–14 mm, shiny, slightly glutinous, glabrous or sparsely or densely whitish-villous.
simple;
stipules early deciduous, whitish-villous;
blade slightly shiny, green to dark green adaxially, ovate to broadly elliptic, 5.5–10.5 × 3–8 cm, margins deeply 1–4 subpalmately lobed, lobes ± triangular, (1–)1.5–2.5 cm wide, basal sinuses deepest, margins finely serrate, secondary veins in 4–6 main pairs, apex acute to acuminate, abaxial surface thinly white-hairy to glabrate, adaxial glabrous.
pinnately compound;
stipules deciduous or persistent, hairs whitish;
blade paler abaxially, shiny, green to dark green adaxially, leaflets 7–13(–15), opposite or subopposite, lanceolate, oblong, narrowly ovate, oblanceolate, or obovate, (3–)4–6.5(–8.7) × 1.5–2.7 cm, l/w ratio 2.1–4.4, margins finely serrate, apex obtuse, acute, or acuminate, surfaces glabrous, leaf and leaflet axils hairy, hairs whitish.
15–60+-flowered, rounded, 3–17.5 cm diam.;
peduncles whitish-villous.
40–200+-flowered, flat-topped to rounded, 5–15 cm diam.;
peduncles sparsely to densely whitish-villous.
whitish-villous.
sparsely to densely whitish-villous (in flower and fruit).
10–17 mm diam.;
hypanthium densely villous, hypanthium plus sepals 5.5–7.5 mm;
sepals 1.5–3.5 mm, margins villous and prominently glandular, glands often relatively thick;
petals white, elliptic, broadly elliptic, or broadly ovate, 4–7 mm;
stamens 20;
carpels adnate to hypanthium, apex conic, styles 2, 3.5–4 mm.
11–13 mm diam.;
hypanthium nearly glabrous or densely villous, hypanthium plus sepals 3–4 mm;
sepals 0.8–2.3 mm, margins lightly to densely whitish-villous, glands absent or sparse and usually inconspicuous;
petals white, ovate, 4–6 mm;
stamens (14–)20;
carpels distinct, apex conic, styles 3 or 4, 2–2.5 mm.
sparsely whitish-villous.
whitish-villous, rarely glabrous with age.
brown, narrowly obovoid, 15–19 × 10–13 mm, dull, not glaucous;
lenticels abundant;
sepals inconspicuous, incurved.
bright orange to reddish orange, globose, subglobose, broadly obovoid, or broadly elliptic, 8–12.1 × 7.5–12.8 mm, shiny, sometimes lightly glaucous;
sepals inconspicuous, incurved.
brown, oblong-lanceoloid, 8.1 × 3.4 mm, slightly asymmetric, slightly flattened.
brown, narrowly ovoid, 3.8–5.4 × 1.7–2.8 mm, slightly asymmetric, slightly flattened.
= 34, 68 (Europe).
= 34, 68.
Sorbus torminalis
Sorbus scopulina
In European gardens, one or more clones of intergeneric hybrids between Pyrus communis and Sorbus are called ×Sorbopyrus auricularis (Knoop) C. K. Schneider. J. Wiśniewska et al. (1969) suggested that S. torminalis may be involved in the parentage of at least one clone.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Sorbus scopulina is variable, especially in leaflet shape, number, and indument. Plants with narrower leaflets were separated as S. angustifolia; plants with broader leaflets were segregated as S. andersonii and S. cascadensis. Densely hairy forms were named S. dumosa. All represent points on a morphologic continuum, united by their shiny leaflets, whitish indument, and western range. Sparsely hairy forms approach the more southern S. californica but have whitish axillary hairs and larger leaflets than that species, which has rufous axillary hairs and leaflets less than 4 cm. Most S. scopulina have shiny hypanthia and fruits. Occasional collections, all within the range of S. sitchensis, are glaucous-fruited. This may be natural variation, or it could represent introgression from S. sitchensis. H. A. McAllister (2005, pers. comm.) found that individuals of S. scopulina from cordilleran Idaho and Arizona were sexual diploids; plants from the Cascade and Coast ranges of British Columbia and Washington were tetraploid and presumably apomictic. Here, these entities are synonymized, awaiting a larger study that might correlate distinct morphologic characteristics with the ploidy levels. J. J. Aldasoro et al. (1998, 2004) noted that some European Sorbus species are both diploid and tetraploid, suggesting that sexual species occasionally produce spontaneous agamospermous individuals.
The intergeneric hybrid ×Amelasorbus jackii Rehder [Amelanchier alnifolia (Nuttall) Nuttall ex M. Roemer × Sorbus scopulina] has been collected in Idaho and Oregon. Foliage of the Idaho collection is very similar to that of Amelanchier, with basal pinnae inconspicuous and infrequent, suggesting that this hybrid may be overlooked.
The illegitimate later homonym Sorbus alaskana G. N. Jones pertains here.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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