A group of shrubs or occasionally trees, both deciduous and evergreen, found most abundantly in the cool temperate regions of N. Asia, especially in China and the Himalaya. Others occur in Europe, and one is British. C. microphyllus is naturalised on the chalk downs near Ventnor, Isle of Wight, also in the counties of Gloucester and Somerset. Seeing how fond birds are of the fruit, it is curious that more naturalised species have not been found. They are closely allied to the thorns (Crataegus), but are easily distinguished by the always entire, not toothed nor lobed leaves, and by having no spines. The flowers are very uniform in size and colour, being nearly always 1⁄3 to 1⁄2 in. in diameter, and either pure white or rose-tinted. They are borne in clusters of varying size, from those of some species that are 2 or 3 in. across, to others with only two or three flowers in the cluster; still others have solitary flowers. The flowering time is mostly in May and June. Whilst some species are very pretty then, the cotoneasters generally are not showy in blossom. Apart from habit and foliage their greatest attraction is in their fruit. In the handsomest sorts this is brilliant red; in. others it is yellowish or brownish, and in a considerable number it is black. They are either globose, egg-shaped, or oval, and vary little in size, averaging about 1⁄4 in. in diameter, and contain two to five nutlets, each consisting of a seed surrounded by the hardened inner wall of the carpel.
The genus Cotoneaster is divided into two well-marked sections:
Sect. Chaenopetalum. – Petals spreading, more or less orbicular. Here belong: C. dammeri; C. frigidus and its allies; C. microphyllus and its allies; C. multiflorus; C. pannosus and its allies, of which C. lacteus is the most important; C. racemiflorus; C. salicifolius and its allies.
Sect. Cotoneaster. – Petals upright, inconspicuous and often tinged with red. Here belong all the other species, but few are widely cultivated in this country, the best known being: C. adpressus; C. bullatus; C. dielsianus; C. distichus; C. franchetii; C. horizontalis; C. simonsii. This section is usually but incorrectly called Orthopetalum.
No shrubs are more easily cultivated than these. They thrive in any soil that is not marshy or water-logged, and are very well adapted for poor soils. They can be propagated quite easily from cuttings made of half-ripened wood about July, and placed in gentle heat. Seeds, too, are plentiful, and can be used, but it is not advisable to use them in some cases, especially where it is desirable that the parent plant, for its brightly coloured fruit or special habit and foliage, should be propagated unchanged. The old practice of grafting them on hawthorn is indefensible. The note on the germination of Crataegus seed applies also to the cotoneasters, though the proportion of species with hard-coated seeds is smaller. For a detailed study see: Contributions of the Boyce Thompson Institute, Vol. 6, pp. 323-38 (1934).
Fireblight. This destructive bacterial disease, which attacks apples, pears and their allies (Rosaceae, subfamily Pomoideae), first made its appearance in south-eastern England in 1956. There is so far no reliable cure for it beyond eradicating the affected plants or cutting out the diseased parts as soon as the onset of the disease is observed. Thanks to the control measures taken the spread of the disease has been checked but if it once took hold very serious losses to fruit growers would result. A number of ornamental plants common in gardens are subject to Fireblight and may become foci of infection from which the disease is spread to neighbouring orchards and commercial plantations.
Of the genera treated in this volume the main sources of infection are Cotoneaster and Crataegus but the following are also subject to the disease: Amelanchier, Aronia, Chaenomeles, and Cydonia. It is not possible here to give full particulars of the symptoms by which Fireblight can be diagnosed but danger signs are: blackening of the flowers; shrivelling of the foliage combined with the formation of wet-looking brown tissue immediately below the surface of the bark. For further information see the note in the Journal of the Royal Horticultural Society, Vol. 93, June 1968, pp. 228-33, and the leaflet published by the Plant Health Branch of the Ministry of Agriculture. Fireblight is a notifiable disease and anyone suspecting its presence should notify the local Plant Health Inspector, either directly or through the branch office of the Ministry of Agriculture. Owners in the Greater London area should write direct to the Ministry at Great Westminster House, Horseferry Road, London, S.W.1.
Between the purely evergreen and the strictly deciduous kinds there are others in which the persistence of the foliage during winter depends upon circumstances. They will retain their leaves in mild winters or warm localities, but lose them where the cold is greater. Vigorous young plants and those growing in good soil will also retain their foliage longer. The taller species from their beauty in fruit, grace of habit, and vigorous constitution, are admirable constituents of the tall shrubbery, but they are still better as isolated specimens on the lawn or in groups in thin woodland. The smaller species make useful and handsome coverings for sloping, sunny banks, whilst the dwarfest of all are very well adapted for the rock garden.
A selection of the best species etc. would include:
Tall Shrubs. – C. affinis var. bacillaris, bullatus, ‘Cornubia’,frigidus, glaucophyllus f. serotinus, henryanus, lacteus, moupinensis, multiflorus, racemiflorus var. soongoricus, simonsii, × watereri ‘John Waterer’.
Medium and Dwarf. – C. adpressus var. praecox, conspicuus, distichus, horizontalis, microphyllus.
For rock garden. – C. adpressus, congestus, microphyllus var. thymifolius.
As a ground carpet. – C. dammeri and ‘Skogholm’, ‘Hybridus Pendulus’, salicifolius (dwarf clones).
Cotoneaster is, for the taxonomist, a genus of great complexity, rivalling in this respect other genera of the Rose family such as Crataegus, Rubus, Sorbus. These difficulties are due in part to the proneness of the cotoneasters to the ‘pseudo-sexual’ method of reproduction known as apomixis, by which seed is set without fertilisation and without the re-shuffling of genes that takes place as a preliminary to normal seed production. This process allows individual variants and hybrids to ‘breed true’ and leads to the formation of microspecies which satisfy most definitions of the classical species of taxonomists and yet may differ one from the other by the most minute differential characters. The treatment of apomicts is a difficult and controversial problem and for this reason it was thought inadvisable to make much use in the present revision of the valuable and interesting studies published on the continent in recent years. The most important are those by Gerhard Klotz, who published in 1957 a general survey of cotoneasters in cultivation (Wiss. Z. Univ. Halle, Math.-Nat., Vol. 6, pp. 945-82), and in 1963 two papers on new or critical species in the C. microphyllus and racemiflorus groups (ibid., Vol. 12, pp. 753-86); and by K. E. Flinck and B. Hylmö (A List of Series and Species in the Genus Cotoneaster, Bot. Notiser, 1966, Vol. 119, Fasc. 3). A more conservative study is: Tse-Tsun Yü, ‘Cotoneasters from the Eastern Himalaya’ (Bull. Brit. Mus., Bot. Ser., Vol. 5, No. 5, 1954).
In previous editions of this work the name Cotoneaster was, following the general custom, treated as a feminine noun. However, Medicus, who first published the name after 1753 (the date from which botanical nomenclature commences), treated it as masculine and this is in accordance with its derivation from cotone (quince) and -aster (a suffix meaning inferior, imperfect, or wild as contrasted with cultivated). The nouns pinaster and oleaster, of similar, derivation, are both masculine. The change of gender has been adopted in all modern works, so there is no alternative but to follow suit in the present edition.
From the Supplement (Vol. V)
Fireblight. A note on this disease appears on page 730. According to recent findings, the pome-fruited genera of the Rosaceae with susceptible species and cultivars are: Cotoneaster, Crataegus, Cydonia, Malus, Pyracantha, × Pyronia, Pyrus, Sorbus and Stranvaesia. See further the illustrated article by Dr Eve Billing in The Garden (Journ. R.H.S.), Vol. 108, pp. 206-10 (1983). Some of the ornamentals most subject to fireblight are being withdrawn from commerce.
So far as Cotoneaster is concerned, those most at risk are the large-leaved species such as C. bullatus and C. salicifolius, and the hybrids deriving from the latter and its relatives with C. frigidus (mentioned under C. frigidus on pages 742-3 of the main work and in this supplement).