Malus

Apple trees are typically 4–12 metres (13–39 feet) tall at maturity, with a dense, twiggy crown. The leaves are 3–10 centimetres (1+1⁄4–4 inches) long, alternate, simple, with a serrated margin.

Flowering occurs in the spring after 50–80 growing degree-days, varying by subspecies and cultivar.^{[citation needed]} The flowers are borne in corymbs and have five petals, which may be white, pink, or red. They are perfect, with usually red stamens that produce copious pollen, and a half-inferior ovary. Many species are self-sterile, requiring cross-pollination between individuals by insects (typically bees, which freely visit the flowers for both nectar and pollen).^[5] A minority of cultivars are self-pollinating, such as "Granny Smith" and "Golden Delicious".^{[citation needed]}

The fruit is a globose pome, varying in size from 1–4 cm (1⁄2–1+1⁄2 in) in diameter in most of the wild species, to 6 cm (2+1⁄4 in) in M. sylvestris sieversii, 8 cm (3 in) in M. domestica, and even larger in certain cultivated orchard apples. The centre of the fruit contains five carpels arranged in a starlike formation, each containing one or two seeds.^{[citation needed]}

The genus Malus is subdivided into eight sections (six, with two added in 2006 and 2008).^{[citation needed]} Several Malus species, including domestic apples, hybridize freely.^[6]

The oldest fossils of the genus date to the Eocene (Lutetian), which are leaves belonging to the species M. collardii and M. kingiensis from western North America (Idaho) and the Russian Far East (Kamchatka), respectively.^[7]

The genus is native to the temperate zone of the Northern Hemisphere.^{[citation needed]}

Crabapples are popular as compact ornamental trees, providing blossom in spring and colourful fruit in autumn. The fruits often persist throughout winter. Numerous hybrid cultivars have been selected.^{[citation needed]}

Some crabapples are used as rootstocks for domestic apples to add beneficial characteristics.^[11] For example, the rootstocks of M. baccata varieties are used to give additional cold hardiness to the combined plants for orchards in cold northern areas.^[12]

They are also used as pollinizers in apples orchards. Varieties of crabapple are selected to bloom contemporaneously with the apple variety in an orchard planting, and the crab trees 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 crabapple flowering branches is placed near the beehives as orchard pollenizers.^{[citation needed]}

Because of the plentiful blossoms and small fruit, crabapples are popular for use in bonsai culture.^[13][14][15]

The seeds contain cyanide compounds.^[25]

Crabapple fruit is not an important crop in most areas. The fruit is rarely eaten raw due to the sour taste resulting from high levels of malic acid. Some species have a woody texture. In some Southeast Asian cultures, they are valued as a sour condiment, sometimes eaten with salt and chilli or shrimp paste.^{[citation needed]} Some varieties of crabapple, such as the 'Chestnut' cultivar, are sweet.^[26]

Crabapples are an excellent source of pectin. Using sugar and spices such as ginger, nutmeg, cinnamon, and allspice, their juice can be made into ruby-coloured crabapple jelly with a full, spicy flavour.^[27] A small portion of crabapples can also be used along with regular apples to make cider.^{[28][self-published source?]}

Applewood gives off a pleasant scent when burned, and smoke from an applewood fire gives an excellent flavour to smoked foods. It is easier to cut when green; dry applewood is exceedingly difficult to carve by hand. It is a good wood for cooking fires because it burns hot and slow, without producing much flame.^{[citation needed]} Applewood is used to make handles of hand saws; in the early 1900s, 2,000,000 board feet of applewood were used annually for this purpose.^[29]