Sorbus scopulina
Sorbus hybrida
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
hybrid mountain ash, oak-leaf mountain-ash, Swedish mountain-ash, Swedish service-tree
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.
single or multistemmed;
bark gray;
winter buds brownish to purple, ovoid to ovoid-conic, 4–10 mm, dull, not glutinous, densely white-villous, at least distally and on scale margins.
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.
proximally pinnately compound, lobed distally;
stipules deciduous or persistent, often white-villous;
blade paler green abaxially, dull green adaxially, ovate to oblong-ovate, rarely oblong, 7–13 × 5–11 cm, pinnately lobed with (1 or)2(or 3) pairs of sessile or decurrent, free, oblong leaflets, terminal leaflets 7–10-lobed, margins serrate at least distally, lobe and leaflet apex acute or obtuse, lateral veins 7–10 pairs, abaxial surface whitish-tomentose.
40–200+-flowered, flat-topped to rounded, 5–15 cm diam.;
peduncles sparsely to densely whitish-villous.
25–75-flowered, flat-topped or rounded, 4.5–10 cm diam.;
peduncles white-villous.
sparsely to densely whitish-villous (in flower and fruit).
white-villous.
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.
10–15 mm diam.;
hypanthium tomentose, hypanthium plus sepals 5–7.5 mm;
sepals 1.5–4 mm, margins usually entire, rarely with inconspicuous glands;
petals white, suborbiculate, broadly obovate, broadly ovate, or broadly elliptic, 5–7 mm;
stamens 20;
carpels 1/2 adnate to hypanthium, apex conic, styles 2 or 3, 2–3 mm.
whitish-villous, rarely glabrous with age.
glabrate to villous.
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.
red, globose to subglobose, 8–15 mm diam., shiny, not glaucous;
sepals inconspicuous, incurved.
brown, narrowly ovoid, 3.8–5.4 × 1.7–2.8 mm, slightly asymmetric, slightly flattened.
red-brown, ovoid, 5–6 × 2 mm, asymmetric, slightly flattened.
= 34, 68.
= 68.
Sorbus scopulina
Sorbus hybrida
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.)
Sorbus hybrida is considered an apomictic tetraploid producing fully fertile pollen and seed and subject to dispersal. An almost undistinguishable European taxon, S. ×thuringiaca (Ilse) Fritsch, often confused with S. hybrida, has been reported for New Hampshire and Vermont. Described as an unstable diploid hybrid between S. aria and S. aucuparia, S. ×thuringiaca has oblong leaves, 1–3(–5) pairs of free leaflets, 10–12(–13) pairs of lateral veins, and produces sterile pollen and relatively few viable seeds. Uncritical reports of escaped S. ×thuringiaca in North America should be considered doubtful; they probably refer to the more likely S. hybrida. The authors have not seen a specimen to document a report of S. hybrida from Montana.
Sorbus hybrida is placed in subg. Sorbus following J. J. Aldasoro et al. (2004), based on leaf division and pome characteristics, including the lack of tanniferous cells in parenchyma, lack of starch, and relatively small sclereid groups.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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