Malus

Malus (/ˈmeɪləs/ or /ˈmæləs/) is a genus of about 30–55 species of small deciduous trees or shrubs in the family Rosaceae, including the domesticated orchard apple (M. pumila syn. M. domestica) – also known as the eating apple, cooking apple, or culinary apple. The other species are commonly known as crabapples, crab apples, crabtrees or wild apples. The genus is native to the temperate zone of the Northern Hemisphere. Apple trees are typically 4–12 m (13–39 ft) tall at maturity, with a dense, twiggy crown. The leaves are 3–10 cm (1.2–3.9 in) 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 a half-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. Several Malus species, including domestic apples, hybridize freely. They 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 (0.39–1.57 in) diameter in most of the wild species, to 6 cm (2.4 in) in M. sylvestris sieversii, 8 cm (3.1 in) in M. domestica, and even larger in certain cultivated orchard apples. The centre of the fruit contains five carpels arranged star-like, each containing one or two seeds. There are about 42 to 55 species and natural hybrids with about 25 from China, of which 15 are endemic. The genus Malus is subdivided into eight sections (six with two added in 2006 and 2008)