|Malus subsp. var.|
Malus, the apples, is a genus of about 30–35 species of small deciduous trees or shrubs in the family Rosaceae. Other studies go as far as 55 species  including the domesticated Orchard Apple, or Table apple as it was formerly called (M. domestica, derived from M. sieversii, syn. M. pumila). The other species and subspecies are generally known as "wild apples", "crab apples", "crabapples" or "crabs".
Apple trees are small, typically 4–12 m tall at maturity, with a dense, twiggy crown. The leaves are 3–10 cm long, alternate, simple, with a serrated margin. The flowers are borne in corymbs, and have five petals, which may be white, pink or red, and are perfect, with usually red stamens that produce copious pollen, and an inferior ovary; flowering occurs in the spring after 50–80 growing degree days (varying greatly according to subspecies and cultivar). Apples require cross-pollination between individuals by insects (typically bees, which freely visit the flowers for both nectar and pollen); all are self-sterile, and (with the exception of a few specially developed cultivars) self-pollination is impossible, making pollinating insects essential. The honeybee and mason bee are the most effective insect pollinators of apples. Malus species, including domestic apples, hybridize freely. Malus species are used as food plants by the larvae of a large number of Lepidoptera species; see list of Lepidoptera that feed on Malus.
The fruit is a globose pome, varying in size from 1–4 cm diameter in most of the wild species, to 6 cm in M. sylvestris sieversii, 8 cm in M. sylvestris domestica, and even larger in certain cultivated orchard apples; among the largest-fruited cultivars (all of which originate in North America) are 'Wolf River' and 'Stark Jumbo' . The centre of the fruit contains five carpels arranged star-like, each containing one to two (rarely three) seeds.
One species, Malus trilobata from southwest Asia, has three- to seven-lobed leaves (superficially resembling a maple leaf) and with several structural differences in the fruit; it is often treated in a genus of its own, as Eriolobus trilobatus.
Crabapples are widely grown as ornamental trees, grown for their beautiful flowers or fruit, with numerous cultivars selected for these qualities and for resistance to disease.
|Standard Cyclopedia of Horticulture|
Malus (Greek for apple). Rosaceae. Apple. Most botanists prefer to unite the apple and pear in the one genus Pyrus; this is the method of Bentham & Hooker in "Genera Plantarum," and of Focke in Engler & Prantl's "Pflanzenfamilien," although the recent excellent work of Schneider, "Handbuch der Laubholzkunde," keeps them distinct, as do some of the recent American authors. The evident botanical distinctions between the two groups are slight, apparently not sufficient for easy or clear determination by the unprofessional student. These differences lie in the usual presence of grit-cells in the fruits of Pyrus and their usual absence in Malus: in the hypanthium of the former being nearly closed by a cushion, and in the latter free or open; in the cavity about the stem of the fruit in Malus, a contrast which does not hold in Pyrus; and in the styles of Pyrus being distinct or nearly distinct, whereas in Malus they are more or less united. The different degrees of union of the styles has been made a basis for distinguishing the named varieties of apples among themselves, and the character does not appear to be important enough to be made the basis of generic separation. It is not impossible that the pears and apples may have had a different phylogenetic origin, but this fact itself would not be sufficient in generic description.—The apples are small trees and bushes, of some fifteen to twenty species in the North Temperate Zone. In this Cyclopedia, the cultivated apple species are described under Pyrus; the names of the leading species under Malus are as follows:
M. sylvestris, Mill.—Pyrus Mains.
M. prunifolia, Borkh. - P. prunifolia.
M. baccata, Borkh.- P. baccata.
M. coronaria, Mill.- P. coronaria.
M. ioensis, Brit.- P. ioensis.
M. Soulardii, Brit.-P. Soulardii.
M. angustifolia, Michx.-P. angustifolia.
M. Halliana, Koehne-P. Halliana.
Pests and diseases
Malus angustifolia—Southern Crab
Malus baccata—Siberian Crabapple
Malus coronaria—Sweet Crabapple
Malus domestica—Orchard Apple
Malus floribunda—Japanese Crabapple
Malus fusca—Oregon Crabapple, Pacific Crabapple
Malus hopa—Flowering Crabapple
Malus hupehensis—Chinese Crabapple
Malus ioensis—Prairie Crab
Malus ×micromalus—Midget Crabapple
Malus pumila syn. Malus sylvestris sieversii—synonyms of Malus sieversii, Asian Wild Apple or Almaty apple
Malus sieversii—Asian Wild Apple or Almaty Apple
Malus sylvestris—European Wild Apple
- ↑ Phipps, J.B. et aL. (1990). "A checklist of the subfamily Maloideae (Rosaceae)". Can. J. Bot. 68: 2209. doi:10.1139/b90-288.
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963