Cotoneaster

Shrubs, subshrubs, or trees, 0–150[–180] dm. Stems 1–25, erect, ascending, spreading to prostrate; bark usually dark gray, smooth; short shoots present or absent; unarmed; glabrous or tomentose to strigose; branches irregular, distichous, divaricate, or spiraled. Leaves persistent, semipersistent, or deciduous, cauline, simple; stipules mostly early deciduous, short-adnate to petiole, linear or narrowly lanceolate, inconspicuous, margins entire; petiole present; blade elliptic to linear, orbiculate, lanceolate, or ovate, [0.3–]0.4–15(–21) cm, leathery to membranous, margins flat or revolute, entire, venation pinnate, 2–14 pairs, surfaces often hairy, rarely glandular. Inflorescences terminal on lateral shoots, 1–150[–200]-flowered, domed or flattened compound panicles, racemes, or flowers solitary, glabrous or hairy; bracts usually present; bracteoles absent. Pedicels usually present. Flowers: perianth and androecium epigynous, 4–15 mm diam.; hypanthium funnelform, cupulate, or campanulate, 1.5–5 mm, glabrous or pilose to tomentose; sepals 5, erect, triangular, often fleshy; petals 5, spreading, white [rarely pale pink], or erect, pink to red or blackish red, spatulate or ± orbiculate, base clawed; stamens (8–)10–20(–23) in 1 or 2 series, shorter than petals; carpels 1–5, distinct, adnate to proximal 1/2 of hypanthium, glabrous or strigose to tomentose, styles 1–5, terminal or lateral, distinct; ovules 2 (only 1 maturing). Fruits pomes, orange to red or purple to black, globose to obovoid or oblong, [3–]4–14[–15] mm, often hairy distally; fleshy, flesh usually yellow, sclereids absent; hypanthium persistent; sepals mostly persistent, erect to incurved or flat; carpels bony; style remnants terminal and projecting from pyrene apex, or lateral, on distal 1/4–1/2 of central adaxial keel. Pyrenes 1–5, without intervening flesh, rarely connate, brown, planoconvex or trigonous, bony. x = 17.

Distribution

Introduced; Eurasia, n Africa, introduced also in Europe, Pacific Islands, Australia.

Discussion

Species ca. 400 (34, including 1 hybrid, in the flora).

A marked concentration of Cotoneaster species is found in the Himalaya and western China. The majority of species (ca. 90%) are apomictic, tetraploid (G. H. Kroon 1975; I. V. Bartish et al. 2001), and breed true when raised from seed.

Cotoneaster was long placed near Crataegus. Based on a reevaluation of flower and fruit characters, it is now believed to be more closely related to Heteromeles and Pyracantha (K. R. Robertson et al. 1991; J. R. Rohrer et al. 1991), but lacks thorns and toothed leaf margins. Recent molecular studies also distance Crataegus from Cotoneaster; as of yet, there is no consensus about the closest allies of Cotoneaster (C. S. Campbell et al. 1995, 2007; R. C. Evans and Campbell 2002). D. Potter et al. (2007) grouped Cotoneaster with Chamaemeles and Malus, but further study is needed to resolve its placement. The genera of Maleae are difficult to organize in a phylogeny, due in part to interfertility, lack of divergence, and reticulate evolution (Campbell et al. 2007).

Plants of Cotoneaster are used by apiarists, as the flowers have abundant nectar and are much loved by bees; the resulting honey is pale golden with a delicate flavor. In Asia, leaves and fruits are used in tea, and the wood for implements. Cotoneaster is used in India and Iran as the source of a sweet mannalike substance high in dextrose. The fruit of C. integerrimus Medikus has been used in the treatment of diarrhea. Many species are ornamentals, with brilliant fall foliage or colorful fruit persisting throughout the winter. The genus is bird-disseminated, mainly by American robins (Turdus migratorius Linnaeus) and cedar waxwings (Bombycilla cedrorum Vieillot) in North America. A few orange- or red-fruited species (C. franchetii, C. lacteus, C. pannosus, and C. simonsii) are weedy on the Pacific coast (J. M. Randall and J. Marinelli 1996; C. C. Bossard et al. 2000). Only C. divaricatus and the black-fruited C. lucidus are widely escaped in the interior.

More than 70 species of Cotoneaster are cultivated in North America, and additional escapes might be expected. Reports of several species in the wild appear to be unfounded. These include C. acutifolius Turczaninow and C. apiculatus Rehder & E. H. Wilson from Pennsylvania (A. F. Rhoads and W. M. Klein 1993; Rhoads and T. A. Block 2000), C. bullatus Bois from British Columbia (J. Pojar 1999), C. hupehensis Rehder & E. H. Wilson from New York (R. S. Mitchell and G. C. Tucker 1997), and C. multiflorus Bunge and C. racemiflorus (Desfontaines) K. Koch from Quebec (J. Cayouette et al. 1983). Without reference specimens it is often difficult to name adventives, given the lack of North American literature.

As with many plants of Maleae, Cotoneaster foliage is variable, yet mature leaf size, shape, texture, and luster on vigorous sterile shoots are usually diagnostic. The leaves of fertile shoots are usually smaller and less typical than those on sterile ones. Shaded plants have larger leaves than individuals in full sun. Deciduous species in flower have smaller leaves than when fruiting. A few species, such as C. gamblei, often hold leaves into January (at least on vigorous sheltered shoots) and key as evergreen shrubs, although naturalized populations in North America will eventually drop most leaves in late winter, especially where exposed. Several species are reported in the literature as semievergreen shrubs (for example, C. horizontalis, C. simonsii), but most of their leaves color and drop by midwinter where they are naturalized on the Pacific coast, so they are keyed as deciduous here. Shrubs with tomentose leaves can be sorted into evergreen and deciduous species by checking for the presence of darkened and weathered tomentum on the abaxial surfaces of overwintered leaves. Sunken (versus superficial) veins are mentioned in the keys and descriptions, always referring to the adaxial leaf surfaces. Collectors should observe this on fresh material and note it on herbarium labels. Sunken veins and wrinkling or bulging between the lateral veins can be obscured when pressing thin-leaved species. The number of veins in the descriptions represents the major lateral veins on one side of the leaf or midvein, most easily observed on the adaxial surface.

The pyrenes are usually pubescent at the apex, if exposed by the navel between the sepals on the summit of the pome. Extracted pyrenes are planoconvex or trigonous (like orange segments). Potentially useful taxonomic characters such as pyrene size, outline, and surface texture are not described here but warrant investigation. The style remnant is usually visible as a small peg or scar on the distal half of the inner surface or central keel of the pyrene; its location is easy to assess if fresh material is available. At least five pomes should be opened to determine the number of pyrenes present.

Identification of most naturalized species requires fruit characters and mature foliage; unfortunately, floral characters are also necessary to separate some species pairs. Floral and fruit dimensions are from fresh material and will be smaller on dried specimens. Floral diameter is provided throughout in subg. Chaenopetalum (Koehne) G. Klotz (species 1–16), which has rotate blossoms with spreading petals. For subg. Cotoneaster (species 17–34), the cupulate flowers are described by their floral length, including hypanthium and the erect petals.

Cotoneaster is properly treated as a masculine name (Yu T. T. 1954), although horticultural works still can be found with feminine endings applied to species epithets.

Key to Groups of Cotoneaster

Key to Species by Group

Group A. Shrubs, prostrate or long-trailing, rarely a few shoots to 30 cm tall; leaves deciduous or persistent, not tomentose.

Group B. Leaves deciduous, abaxial surfaces tomentose.

Group C. Shrubs or trees, erect; leaves persistent, abaxial surfaces tomentose.

Group D. Stems erect; leaves persistent, glabrous or sparsely hairy abaxially.

Group E. Stems erect; leaves deciduous, glabrous abaxially or hairy, not densely tomentose; pomes black or purple-black.

Group F. Leaves deciduous, abaxial surfaces glabrous or hairy, not densely tomentose; pomes orange or red, dark red, or red-purple.

Selected References

Flinck, K. E. and B. Hylmö. 1966. A list of series and species in the genus Cotoneaster. Bot. Not. 119: 445–463.

Fryer, J. and B. Hylmö. 2009. Cotoneasters: A Comprehensive Guide to Shrubs for Flowers, Fruit, and Foliage. Portland.

Klotz, G. 1957. Uebersicht ueber die in Kulture befindlichen Cotoneaster-Arten und -Formen. Wiss. Z. Martin-Luther-Univ. Halle-Wittenberg, Math.-Naturwiss. Reihe 6: 945–982.

Klotz, G. and T. Krügel. 1983. Zur zytologischen Struktur der Gattung Cotoneaster Medik. II. Wiss. Z. Friedrich-Schiller-Univ. Jena, Math.-Naturwiss. Reihe 32: 901–907.

Rehder, A. J. and E. H. Wilson. 1913. Cotoneaster. In: C. S. Sargent, ed. 1913–1917.

Plantae Wilsonianae.... 3 vols. in parts. Cambridge, Mass. Vol. 1, pp. 154–177.

Keys

Key to Groups of Cotoneaster

1	Shrubs, prostrate or long-trailing, rarely a few shoots to 30 cm tall	Group A
1	Shrubs or trees, erect, more than 30 cm tall	> 2
2	Mature leaves tomentose abaxially (hairs obscuring veins and most or all of surfaces)	> 3
2	Mature leaves glabrous or slightly hairy abaxially (surfaces easily visible)	> 4
3	Leaves deciduous	Group B
3	Leaves persistent	Group C
4	Leaves persistent	Group D
4	Leaves deciduous	> 5
5	Pomes black or dark purple; styles and pyrenes 1–3	Group E
5	Pomes orange to red, dark red, or red-purple; styles and pyrenes (1 or)2–5	Group F

Group A. Shrubs, prostrate or long-trailing, rarely a few shoots to 30 cm tall; leaves deciduous or persistent, not tomentose

1	Leaves deciduous, blades chartaceous, margins slightly undulate, not revolute; petals erect, dark red.	Cotoneaster adpressus
1	Leaves persistent, blades coriaceous, margins slightly revolute, not undulate; petals spreading, white	> 2
2	Styles and pyrenes 2(or 3); leaf blades 5–14 mm.	Cotoneaster cochleatus
2	Styles and pyrenes 4 or 5; leaf blades 13–43 mm.	Cotoneaster dammeri

Group B. Leaves deciduous, abaxial surfaces tomentose

1	Pomes purple-black, dark red, or ruby to maroon	> 2
1	Pomes bright red or orange-red	> 3
2	Pomes dark red or ruby to maroon; petals spreading, white; anthers purple to blackish purple; styles and pyrenes 1(or 2) .	Cotoneaster monopyrenus
2	Pomes purple-black; petals erect, greenish white with pink or red; anthers white; styles and pyrenes 2–4.	Cotoneaster melanocarpus
3	Filaments pink or pale pink; leaf blades: abaxial surfaces villose-strigose or sparsely to moderately tomentose.	Cotoneaster tengyuehensis
3	Filaments red or dark red; leaf blades: abaxial surfaces densely tomentose	> 4
4	Pomes orange-red.	Cotoneaster qungbixiensis
4	Pomes bright red.	Cotoneaster dielsianus

Group C. Shrubs or trees, erect; leaves persistent, abaxial surfaces tomentose

1	Shrubs, 0.5(–1.5) m; leaf blades 5–11 mm.	Cotoneaster hodjingensis
1	Shrubs or trees, 1–9 m; leaf blades 15–120 mm	> 2
2	Leaves: lateral veins ± superficial, rarely faintly sunken, adaxial surfaces flat between lateral veins; styles and pyrenes (1 or)2	> 3
2	Leaves: lateral veins sunken, adaxial surfaces bulging or flat between lateral veins; styles and pyrenes 2–5	> 5
3	Pomes slightly glaucous, sepals flat to incurved; flowers (7–)10–11 mm diam	Cotoneaster crispii
3	Pomes not glaucous, sepals suberect; flowers 6–10 mm diam	> 4
4	Leaf blades 15–35(–39) x 10–19(–26) mm; flowers 8.5–10 mm diam.	Cotoneaster pannosus
4	Leaf blades 35–77 × 15–35 mm; flowers 6–6.5(–9) mm diam.	Cotoneaster vestitus
5	Petals spreading, creamy white; anthers red-purple; styles and pyrenes 2; leaf blades obovate to elliptic, rarely broadly elliptic.	Cotoneaster lacteus
5	Petals erect, pink or red; anthers white, pink, or purplish pink; styles and pyrenes (2 or)3–5 (always some with more than 2); leaf blades ovate to elliptic	> 6
6	Anthers white	> 7
6	Anthers pink to purplish pink or mostly white with pink-tinged sutures	> 8
7	Filaments pink or pale pink, whitish distally; pomes bright red; leaves sparsely to moderately tomentose abaxially.	Cotoneaster tengyuehensis
7	Filaments dark red, at least proximally; pomes orange-red; leaves densely tomentose abaxially.	Cotoneaster qungbixiensis
8	Filaments pink, distally white; anthers pink to purplish pink; leaves usually flat adaxially between lateral veins; pomes obovoid, bases rounded or cuneate to obconic, straight-sided.	Cotoneaster franchetii
8	Filaments red; anthers white with pink-tinged sutures; leaves usually bulging slightly adaxially between lateral veins (less obvious on shaded shoots); pomes subglobose to depressed-globose or globose, bases rounded.	Cotoneaster sternianus

Group D. Stems erect; leaves persistent, glabrous or sparsely hairy abaxially

1	Shrubs, usually less than 0.8 m; leaf blade margins revolute	> 2
1	Shrubs or trees, 1–10 m; leaf blade margins flat or revolute	> 4
2	Leaf blades usually oblanceolate or oblong; pomes dull or slightly shiny, glaucous.	Cotoneaster integrifolius
2	Leaf blades usually elliptic to narrowly elliptic; pomes shiny, not glaucous	> 3
3	Leaf blades 6–12(–20) x 2–6(–8) mm, adaxial surfaces grayish green, dull to slightly shiny; styles and pyrenes 2(or 3).	Cotoneaster conspicuus
3	Leaf blades 10–27 × 4–12 mm, adaxial surfaces dark green, shiny; styles and pyrenes 2–4(or 5) (always some with more than 2).	Cotoneaster ×suecicus
4	Leaf blades: adaxial surfaces flat between lateral veins, veins superficial or essentially so; styles and pyrenes (1 or)2	> 5
4	Leaf blades: adaxial surfaces wrinkled or bulging between lateral veins, or veins deeply sunken; styles and pyrenes 2–5	> 6
5	Leaf blades 25–46 mm, adaxial surfaces dull, slightly glaucous; pomes 6–8 mm, globose or subglobose.	Cotoneaster crispii
5	Leaf blades (25–)50–127 mm, adaxial surfaces shiny, not glaucous; pomes 8.5–12.8 mm, obovoid, rarely subglobose.	Cotoneaster gamblei
6	Styles and pyrenes usually 3–5; petals erect, pink to red; anthers white.	Cotoneaster tengyuehensis
6	Styles and pyrenes usually 2 or 3; petals spreading, white or creamy white; anthers red-purple	> 7
7	Leaf blades shiny adaxially, narrowly elliptic to elliptic-lanceolate, 3–4 times as long as wide, margins strongly revolute, apices gradually tapered, acute or acuminate; styles and pyrenes 2 or 3(or 4); pomes maturing in October.	Cotoneaster salicifolius
7	Leaf blades dull or slightly shiny adaxially, obovate to elliptic, rarely broadly elliptic, 2 times as long as wide, margins flat or slightly revolute, apices short-tapered, acute, acuminate, or obtuse; styles and pyrenes 2; pomes maturing in November.	Cotoneaster lacteus

Group E. Stems erect; leaves deciduous, glabrous abaxially or hairy, not densely tomentose; pomes black or purple-black

1	Leaves usually bulging between lateral veins, veins sunken (easily obscured on pressed plants)	> 2
1	Leaf blades: adaxial surfaces flat between lateral veins, veins superficial or slightly sunken	> 3
2	Vigorous shoots with leaf tips short-acuminate or acute; pomes glaucous.	Cotoneaster lucidus
2	Vigorous shoots with leaf tips attenuate to long-acuminate; pomes not glaucous.	Cotoneaster villosulus
3	Styles and pyrenes 1 or 2; petals white, spreading, usually with hair tuft	> 4
3	Styles and pyrenes 2–4; petals pink to red or purple, erect, glabrous	> 5
4	Leaves of vigorous shoots 1.5 times as long as wide; pomes: sepal margins sparsely hairy.	Cotoneaster monopyrenus
4	Leaves of vigorous shoots 2 times as long as wide; pomes: sepal margins glabrous.	Cotoneaster transens
5	Leaf blades 8–28 mm; fall leaves turning bright red and gold; styles and pyrenes 2(or 3).	Cotoneaster nitens
5	Leaf blades 33–45 mm; fall leaves lacking notable color; styles and pyrenes 2–4.	Cotoneaster melanocarpus

Group F. Leaves deciduous, abaxial surfaces glabrous or hairy, not densely tomentose; pomes orange or red, dark red, or red-purple

1	Adaxial surfaces of fresh leaves strongly wrinkled or bulging between lateral veins (easily obscured when pressed); styles and pyrenes (4 or)5.	Cotoneaster rehderi
1	Adaxial surfaces of fresh leaves flat between lateral veins, sometimes faintly bulging (some taxa with faintly sunken midvein or wavy margins); styles and pyrenes (1 or)2–5	> 2
2	Leaf blades 4–30(–36) mm	> 3
2	Leaf blades (21–)30–150 mm	> 7
3	Shrubs 1.5–4(–6) m; pomes usually cylindric to obovoid (proportionally narrower)	> 4
3	Shrubs 0.5–1 m; pomes usually broadly obovoid	> 5
4	Plants ± strict or ascending, lateral branches mostly suppressed, short, ± straight; stamens 20 (found under calyx in fruit, with careful dissection); pomes bright orange to orange-red, usually obovoid; styles and pyrenes (2 or)3–5; leaf blades on vigorous shoots usually broadly elliptic to ovate.	Cotoneaster simonsii
4	Plants spreading with rounded shape, lateral branches well developed, usually long, arching; stamens 10–15; pomes dark red to ruby (finally blackish red), cylindric, oblong-ellipsoid, or narrowly obovoid; styles and pyrenes (1 or)2(or 3); leaf blades on vigorous shoots usually elliptic or broadly elliptic.	Cotoneaster divaricatus
5	Leaf blades on vigorous shoots usually broadly elliptic.	Cotoneaster horizontalis
5	Leaf blades on vigorous shoots usually broadly obovate to orbiculate	> 6
6	Leaf blades on vigorous shoots obovate-orbiculate; pomes bright red; sepals sparsely pilose.	Cotoneaster atropurpureus
6	Leaf blades on vigorous shoots orbiculate, sometimes broadly obovate; pomes orange-red; sepals glabrous.	Cotoneaster hjelmqvistii
7	Leaf blades (25–)50–150 mm; anthers purple, red-purple, or black; pomes red to purplish red or maroon to purple-black	> 8
7	Leaf blades usually less than 50 mm; anthers white; pomes orange to dark red	> 10
8	Pomes maroon to purple-black, sepals sparsely villous, margins glabrous.	Cotoneaster transens
8	Pomes red, sepals densely villous, margins tomentose	> 9
9	Pomes 4–6 × 4–5 mm, sepals erect or ascending; pedicels (and peduncles) densely tomentose.	Cotoneaster frigidus
9	Pomes 8.5–12.8 × 8–12 mm, sepals flat; pedicels (and peduncles) sparsely villose-strigose.	Cotoneaster gamblei
10	Petals spreading; flowers 12–14 mm diam.; petioles 5–8 mm.	Cotoneaster magnificus
10	Petals erect or erect-incurved; flowers 4–10 mm diam.; petioles 1–5 mm	> 11
11	Styles and pyrenes (2 or)3–5	> 12
11	Styles and pyrenes 2(or 3)	> 13
12	Pomes orange to orange-red; sepals erect or ascending, rarely nearly flat (not meeting over and obscuring pome summit), navel open; flowers pendent.	Cotoneaster simonsii
12	Pomes bright red; sepals flat (meeting over and obscuring pome summit), navel closed; flowers erect or ascending.	Cotoneaster tengyuehensis
13	Pomes bright to dark red; leaves on vigorous shoots elliptic, broadly elliptic, or ovate, sometimes suborbiculate.	Cotoneaster fangianus
13	Pomes bright orange-red; leaves on vigorous shoots elliptic to narrowly ovate (usually proportionally narrower).	Cotoneaster miniatus