Sorbaria (Seringe ex de Candolle) A. Braun, 1860

Song, Jun-Ho & Hong, Suk-Pyo, 2021, A taxonomic revision of the genus Sorbaria (Rosaceae) with a new infrageneric classification based on morphology, micromorphology, and palynology, Phytotaxa 487 (1), pp. 1-25 : 7-8

Key to the species of Sorbaria

- Shrub up to 7 m, usually more than 3 m; follicles and ovaries glabrous; inflorescences pendulous, widely spreading branches; sepals semicircular, apex obtuse, broader than long, glabrous; stamens usually 20, equal to the petals ...........................................3

2. Shrub 1–3 m; inflorescences composed of numerous flowers; flowers 5–10 mm in diameter; petals 1.3–5.9 mm long; sepals 0.7– 2.5 mm long; Northern China (including Inner Mongolia), Japan, Korea, and Russian Far East (including Kamchatka Peninsula). .......................................................................................................................................................................................... S. sorbifolia

- Shrub 0.2–0.5 m; inflorescences composed of few flowers; flowers 10–15 mm in diameter; petals 4.0– 6.5 mm long; sepals 1.4–3.4 mm long; Russian Far East (Lake Baikal)............................................................................................................................ S. pallasii

3. Style recurving, fixed at or near the apex of the follicle; Afghanistan, India, Nepal, and Pakistan................................ S. tomentosa

- Style fixed much below the apex of the follicle; Central and southern China, Japan, and Korea..................................... S. kirilowii

. Sorbaria sorbifolia (Linnaeus) A. Braun in Ascherson (1860: 177)

≡ Spiraea sorbifolia Linnaeus (1753: 490) . Basilima sorbifolia (Linnaeus) Rafinesque (1838: 75) . Schizonotus sorbifolius (Linnaeus) Lindley ex Steudel (1841: 531) , nom. inval. Type:—Unknown location. Unknown specific location, date unknown, Linnaeus s.n. (lectotype, designated by Rahn, 1989: BM 651-15, photo!).

Description: —Shrubs, erect, 1–3 m tall. Branches erect; branchlets and rachis sparsely to moderately pubescent with stellate hairs, short simple hairs, glandular hairs. Leaves: petioles 1.0–(3.8)– 7.2 cm long; blades 11–(21)– 35 cm long in outline; leaflets 9–(18)–29, narrowly lanceolate to ovate-lanceolate, apex acuminate or caudate, base sub-rounded to cuneate, margins double serrate, adaxial surface glabrous or rarely pubescent with glandular hairs on midveins, abaxial surface glabrous or sparsely to densely pubescent with stellate hairs, glandular hairs, and moderately to densely pubescent with short simple hairs on midveins; blade of terminal leaflets 1.4–(4.9)–9.6 × 0.5–(1.5)– 3.1 cm (length × width), lateral veins 9–(21)–36 pairs; blade of lateral leaflets 2.5–(6.0)–10.4 × 0.8–(1.6)– 3.1 cm, lateral veins 12–(24)–39 pairs. Inflorescences erect, narrowly spreading branches, 7.6–(18)–32 × 2.1–(6.5)– 14 cm, peduncle and pedicels sparsely to moderately pubescent with stellate hairs, glandular hairs. Flowers 5–(7)– 10 mm in diameter; sepals triangular, apex acute, 0.7–(1.5)– 2.5 mm long, outer surface sparsely pubescent with stellate hairs; petals 1.3–(3.0)– 5.9 mm long; stamens 40–50, 2.9–(5.2)– 7.5 mm long, 1.5–2 × as long as petals; ovary densely pubescent with short simple hairs. Follicles 4.1–(5.0)–7.7 × 2.6–(3.9)– 5.3 mm, densely pubescent with short simple hairs. Seeds narrowly ellipsoid, 3.8–(4.8)–6.1 × 0.3–(0.5)– 0.8 mm.

Notes: —This species was first recognized as two infraspecific taxa (α, glabra; β, stellipila ) based on the presence or absence of stellate and simple hairs ( Maximowicz 1879). However, Rahn (1989) did not recognize any infraspecific taxa, although he mentioned that the type specimens and western distribution specimens had no stellate hairs, and the eastern distribution specimens had stellate hairs. In the present study, three varieties were proposed based on the distribution patterns and a previous numerical study ( Song & Hong 2018b).

1. Leaflet’s abaxial surface glabrous; Russian Far East (including Kamchatka Peninsula), Inner Mongolia, Europe, and North America ...............................................................................................................................................1a. S. sorbifolia var. sorbifolia

- Leaflet’s abaxial surface densely stellate and glandular hairy ...........................................................................................................2

2. Leaflet’s abaxial surface densely pubescent with stellate hairs (average 41.7/ 2 mm 2) rather than glandular hairs (average 5.4/ 2 mm 2); Northern China, Korea, and Japan............................................................................................. 1b. S. sorbifolia var. stellipila

- Leaflet’s abaxial surface densely pubescent with glandular hairs (average 57.6/ 2 mm 2) rather than stellate hairs (average 7.7/ 2 mm 2); Korea only ...........................................................................................................................1c. S. sorbifolia var. glandulifolia a. Sorbaria sorbifolia (L.) A. Braun var. sorbifolia