Sorbus decora
Sorbus sitchensis
northern mountain-ash, showy mountain-ash, sorbier plaisant
Sitka mountain-ash, western mountain ash
1–4+;
bark gray to bronze;
winter buds purplish at maturity, shiny, conic, 10–20 mm, glutinous, scales ciliate to moderately (densely) villous, hairs primarily rufous.
1–8;
bark initially reddish purple to brownish gray, becoming grayish red;
winter buds red-purple to red-brown, conic to ovoid, 8–13 mm, dull, slightly glaucous, not glutinous, sparsely or densely villous, hairs primarily rufous.
pinnately compound;
stipules deciduous, sometimes persistent, glabrous or with whitish and/or rufous hairs;
blade paler abaxially, dull green to bluish green adaxially, leaflets (11–)13–17, opposite, elliptic, oblong to oblong-ovate, 4–7(–8) × 1.5–2.5 cm, l/w ratio 2.4–3.2(–3.6), margins serrate, sometimes serrulate, at least in distal 1/2 and often almost to base, apex abruptly short-acuminate, cuspidate, acute, or obtuse, surfaces essentially glabrous or sparsely (moderately) villous at flowering, usually glabrescent thereafter, sometimes persistently villous along midveins abaxially;
leaflet axils and petiole bases glabrous or with some rufous and/or whitish hairs adaxially.
pinnately compound;
stipules persistent, sometimes deciduous, hairs rufous;
blade paler abaxially, dull blue-green, usually slightly glaucous, rarely faintly shiny adaxially, leaflets 7–13, opposite, sometimes subopposite, oblong to narrowly elliptic, sometimes oblanceolate, ovate, or obovate, 1.8–6 × 0.6–2.5 cm, l/w ratio 1.9–3.5, margins entire or finely to coarsely serrate, sometimes doubly serrate, apex obtuse or acute, surfaces soon glabrous, leaf and leaflet axils hairy, hairs rufous.
75–400+-flowered, flat-topped or rounded, 6–15 cm diam.;
peduncles sparsely to moderately (densely) villous.
12–80-flowered, rounded, 2–8 cm diam.;
peduncles glabrous, glaucous, or sparsely to densely villous, hairs primarily rufous.
sparsely to moderately (densely) villous.
glabrous, glaucous, or sparsely to densely villous, hairs primarily rufous.
(7–)8–12 mm diam.;
hypanthium glabrous or sparsely villous proximally, hairs whitish or rufous, hypanthium plus sepals 2.5–3.5 mm;
sepals 1–1.5(–2) mm, margins entire, often with a few thick glands;
petals white, orbiculate to obovate, (3–)3.5–5 mm;
stamens 15–20;
carpels 1/2 adnate to hypanthium, apex conic, styles 3 or 4, 1.5–2.5 mm.
11–17 mm diam.;
hypanthium glabrous, glaucous, hypanthium plus sepals 3–4 mm;
sepals 1–2.2 mm, margins lightly to moderately ciliate, hairs rufous or whitish, infrequently glandular;
petals white, rarely pinkish, rhombic to ovate, 4–7.5 mm;
stamens 15–20;
carpels distinct, apex concave, depressed, or slightly conic and truncate, styles 3–5, 1.5–3.2 mm.
sparsely to moderately villous, rarely glabrous.
glabrous, glaucous, or villous.
bright red, globose to subglobose, (5–)7–11 mm diam., shiny or dull, often glaucous when dried;
sepals inconspicuous, incurved.
pinkish red or red (often appearing slightly purplish), subglobose to broadly elliptic or obovoid, 7–13 × 7–13 mm, dull, glaucous;
sepals inconspicuous, incurved.
brown, lanceoloid, 4.5–5 × 1.5–2 mm, slightly asymmetric, slightly flattened.
red-brown, ovoid to ovoid-lanceolate, oblong or elliptic, 3.4–5 × 2.2–2.9 mm, symmetric or trigonous, slightly flattened.
= 68.
Sorbus decora
Sorbus sitchensis
Sorbus decora reputedly flowers about one week later than S. americana. The two are sometimes confused when one is not familiar with the smaller flowers and fruits, and the distinctly longer and notably acuminate leaflets of S. americana. Leaflet length/width ratios greater than 3.2 are sometimes observed on narrower leaflets of S. decora, and a range of representative leaflets need to be sampled before determination. Another species frequently confused with S. decora is S. aucuparia, characterized by ovoid, usually densely whitish-villous and not glutinous winter buds as well as densely villous flowering pedicels and hypanthia, and often abaxially tomentose leaflets at flowering. The teeth on margins of leaves in S. decora are more finely pointed and sharper than those of S. aucuparia, and the apical tooth is often distinctly prolonged in S. decora; it is no more conspicuous than the lateral ones in S. aucuparia (E. G. Voss 1972–1996, vol. 2). The leaflets of S. aucuparia are reported to be minutely papillose abaxially (visible at 100× ); those of S. decora and other members of sect. Commixtae are not papillose (H. A. McAllister 2005). Sorbus decora is reported to be extirpated from Indiana.
Chromosome counts of 2n = 34 were reported by Á. Löve and D. Löve (1965, 1982b) for Sorbus decora. Doubt exists about the identity of the material that they sampled, as the only voucher specimen retraced (Á. & D. Löve 6559, COLO, WIN), although only vegetative and juvenile, is nonetheless referable to S. aucuparia. These doubtful chromosome counts also formed the basis for the recognition of S. groenlandica (Löve and Löve 1965b), reputedly of Greenland, coastal Labrador, and alpine and subalpine regions of northeastern North America, which apparently differed from S. decora with a chromosome count of 2n = 68 (T. W. Böcher and K. Larsen 1950; K. Holmen in C. A. Jørgensen et al. 1958). Reliable S. decora chromosome counts by H. A. McAllister (2005) of three wild collections (Dundas, Ontario; St. Anne de Beaupré, Quebec; Narsarsuaq Greenland) and two of cultivated material rendered this proposition untenable with consistent counts of 2n = 68. Further, critical examination of herbarium specimens from Greenland yielded no consistent morphologic character to separate S. decora from S. groenlandica, though leaflet and fruit size in the latter tended to be relatively smaller.
A naturally occurring putative intergeneric hybrid, ×Sorbaronia arsenii (Britton ex L. Arsène) G. N. Jones, synonym Pyrus ×arsenii (Britton ex L. Arsène) L. Arsène [= Aronia ×prunifolia (Marshall) Rehder × Sorbus decora], is known from New Brunswick, Nova Scotia, Prince Edward Island, St. Pierre and Miquelon, Quebec, and, possibly, Newfoundland. The hybrid is a 10–25 dm shrub with finely serrulate, partially pinnate leaves containing (0 or)1–3 pairs of reduced, distinct leaflets proximally and a much larger, 1–3-lobed terminal segment. The midvein on the adaxial surface of the terminal leaflet may be irregularly glandular or eglandular. A possible variant of this hybrid (parentage unconfirmed), much closer to Sorbus in appearance, is found in southwestern Newfoundland. It possesses finely serrulate, almost fully pinnate leaves, often with four or five pairs of distinct leaflets, the distal first or second leaflet pairs more or less pinnatifid or partially fused to the terminal leaflet. The hypanthium and abaxial surface of the sepals are villous, the anthers are pink or red, and the pomes are usually red, though some are reported to be blackish in age, often with some tomentum persisting on the abaxial surface of the persistent sepals.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 2 (2 in the flora).
The other western Sorbus with rufous indument in the leaf and leaflet axils is S. californica, which differs in its smaller, shinier leaflets, less hairy inflorescences, and shiny winter buds. The winter buds of S. sitchensis are hairier and less scaly at the summit, also glaucous and never shiny or glutinous. In the field, the fresh fruits of S. sitchensis are often pinkish red; fruits of S. californica and S. scopulina are generally orange-red.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaflet margins toothed apically, serrate for more than 1/2 their length; petals white. | var. sitchensis |
1. Leaflet margins entire or toothed apically, serrate for less than 1/2 their length; petals white or pinkish. | var. grayi |
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