9. Sorbus sambucifolia (Chamisso & Schlechtendal) M. Roemer, Fam. Nat. Syn. Monogr. 3: 139. 1847.
Aleutian mountain ash
Pyrus sambucifolia Chamisso & Schlechtendal, Linnaea 2: 36. 1827
Shrubs, 10–20 dm. Stems 1–8; bark gray; winter buds blackish red to black, conic, 7–18 mm, shiny, slightly glutinous, sparsely villous distally, hairs primarily rufous. Leaves pinnately compound; stipules sometimes persistent, margins and surface hairy, hairs rufous; blade paler abaxially, shiny, green to dark green adaxially, leaflets 7–11, opposite or subopposite, lanceolate, sometimes narrowly elliptic, elliptic, oblong, or oblanceolate, 2.5–6.5 × 0.9–2.5 cm, l/w ratio 1.9–3.8, margins serrate, apex usually acute to acuminate or attenuate, sometimes obtuse, surfaces soon glabrous; leaf and leaflet axils hairy, hairs rufous. Panicles 6–23-flowered, rounded, 2.5–7 cm diam.; peduncles sparsely rufous-villous. Pedicels sparsely rufous-villous. Flowers 10–15 mm diam.; hypanthium glabrous, hypanthium plus sepals (4.5–)5–6 mm; sepals 1.5–2.9 mm, margins usually villous, hairs white and reddish mixed [white], rarely sparsely glandular; petals white to pinkish, orbiculate or ovate, 4–5 mm; stamens 20; carpels almost completely adnate to hypanthium, apex truncate or slightly conic, styles 4 or 5, 1.5–3.5 mm. Infructescences glabrous. Pomes red, ellipsoid, 10–12 × 7–9 mm, shiny, not glaucous; sepals prominent, erect. Seeds dark brown, lanceoloid, 4 × 2 mm, symmetric, not flattened. 2n = 34 (Asia).
Flowering spring; fruiting fall. Slopes and meadows; 0–100 m; Alaska; e Asia (Japan, Russian Far East [Commander Islands, Kamchatka, Kuril Islands]).
In North America, Sorbus sambucifolia is known only from the four westernmost islands of the Aleutians, where it is allopatric from all other Sorbus. Sorbus scopulina is known from farther east in the Aleutians; sterile specimens differ in their whitish, not rufous indument, and the less deeply sunken reticulate venation on the adaxial surfaces of the leaflets.