56. Cotoneaster Medikus, Philos. Bot. 1: 154. 1789.
[Latin cotoneum, quince, and -aster, incomplete resemblance, alluding to similarity of leaves in some species]
Jeanette Fryer, Bertil Hylmö†, Peter F. Zika
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.
Species ca. 400 (34, including 1 hybrid, in the flora): introduced; Eurasia; n Africa; introduced also in Europe, Pacific Islands, Australia.
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 Species by Group
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.