A genus of some twenty-five to thirty deciduous trees, including a few shrubs, distributed over the temperate parts of the northern hemisphere. Leaves simple, occasionally lobed. Flowers usually in umbel-like clusters, white to various shades of pink or purplish. Stamens fifteen to fifty, anthers usually yellow. It differs from Pyrus, with which it was long generically united, by the styles being united at the base – free in Pyrus. The fruits in most species are crowned with the persistent calyx and vary in shape from rounded to ovoid, but are never truly pear-shaped as in Pyrus. In Pyrus, moreover, the flesh of the fruit contains stone-cells (grit-cells). In Malus these are absent except in a few anomalous species, notably M. prattii, M.yunnanensis, M. tschonoskii, M. florentina, and M. trilobata.
So far as is known there is no hybrid between Malus and Pyrus, nor with any other of the genera once included in Pyrus, and the fact that it will not readily intergraft with them further shows that Malus is more distinct from the other sections of the old genus Pyrus than was once imagined. It was the incompatibility of the apple and pear in grafting that chiefly led Philip Miller to maintain the genus Malus in defiance of Linnaeus, who had sunk it in Pyrus. ‘I shall therefore beg leave,’ he wrote, ‘to continue the separation of the Apple from the Pear, as hath been always practised by the botanists before his time.’
Many of the crabs rank highly as ornamental trees. In all the range of flowering trees and shrubs there is nothing more beautiful and effective than the best of this group, such as M. spectabilis and M. floribunda. In regard to fruit the genus contains many valuable species and hybrids, such as M. × robusta, ‘John Downie’, ‘Golden Hornet’, ‘Red Sentinel’ and many others.
The species of Malus hybridise with each other, so that with many one cannot rely on seeds to reproduce the parent exactly. Some crabs can be rooted from cuttings made of leafless shoots in early winter, and put in a cold frame, but most of them are increased by grafting on the various stocks used in nurseries for garden apples.
Attention must be called to the fact that the crab apples, like all members of the section Pomoideae of the Rose family, are subject to attack by the devastating disease ‘fire-blight’, for which see the note in Vol. I, p. 730.
Useful notes on the species and hybrids grown in Britain will be found in the article by H. S. J.Cranein Journ. R.H.S., Vol. 86 (1961), pp. 160-167; and in Hillier’s Manual of Trees and Shrubs. An assessment by H. J. Grootendorst, based on trials at Boskoop, Holland, was published in Dendroflora, Vol. 1 (1964). A valuable American work is: A. F. Den Boer, Ornamental Crab Apples, published by the American Association of Nurserymen in 1959. In Dr Donald Wyman’s Trees for American Gardens (ed. 1965) there is an extensive section devoted to Malus.
For the hybrids see the special section starting on p. 714.
From the Supplement (Vol. V)
The report on trials in Holland published in the first issue of Dendroflora (1964) is superseded by a later report by P. Lombarts, published in No. 21 of the same periodical (1984), pp. 39-62, with a summary in English.