Malus

Malus, the apples, is a genus of about 30-35 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated Orchard Apple, or Table apple as it was formerly called (M. sylvestris domestica, derived from M. sylvestris sieversii, syn. M. pumila). The other species and subspecies are generally known as "wild apples", "crab apples", "crabapples" or "crabs", this name being derived from their small and tart fruit^{[citation needed]}. Cultivars such as 'Whitney' have been independently domesticated for better fruit quality^{[citation needed]}.

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The genus is native to the temperate zone of the Northern Hemisphere, in Europe, Asia and North America.

  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^{[citation needed]} 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.

Uses

  For Malus sylvestris domestica, see Apple. The fruit of the other species is not an important crop in most areas, being extremely sour and (in some species) woody, and is rarely eaten raw for this reason. However, crabapples are an excellent source of pectin, and their juice can be made into a ruby-coloured jelly with a full, spicy flavour^[1]. A small percentage of crab apples in cider makes a more interesting flavour.

Crabapples are widely grown^{[citation needed]} as ornamental trees, grown for their beautiful flowers or fruit, with numerous cultivars selected for these qualities and for resistance to disease.

Some crab apples are used as rootstocks for domestic apples to add beneficial characteristics^{[citation needed]}. For example, Siberian crab rootstock is often used^{[citation needed]} to give additional cold hardiness to the combined plant for orchards in cold northern areas.

They are also used as pollinators in apple orchards. Varieties of crab apple are selected to bloom contemporaneously with the apple variety in an orchard planting, and the crabs are planted every sixth or seventh tree, or limbs of a crab tree are grafted onto some of the apple trees. In emergencies, a bucket or drum bouquet of crab apple flowering branches are placed near the beehives as orchard pollenizers. See also Fruit tree pollination.

References

• Germplasm Resources Information Network: Malus
• Flora of China: Malus
• Virginia Cooperative Extension - Disease resistant crabapples
• Ontario Ministry of Agriculture and Food - Crabapple pollenizers for apples

1. ^ Rombauer, I.; Becker, M. R., & Becker, E. [2002]. All About Canning & Preserving (The Joy of Cooking series). New York: Scribner, p. 72. ISBN 0-7432-1502-8.