The apple is a tree and its pomaceous fruit, of the species Malus domestica in the rose family Rosaceae. It is one of the most widely cultivated tree fruits. It is a small deciduous tree reaching 5-12 m tall, with a broad, often densely twiggy crown. The leaves are alternately arranged, simple oval with an acute tip and serrated margin, slightly downy below, 5-12 cm long and 3-6 cm broad on a 2-5 cm petiole. The flowers are produced in spring with the leaves, white, usually tinged pink at first, 2.5-3.5 cm diameter, with five petals. The fruit matures in autumn, and is typically 5-9 cm diameter (rarely up to 15 cm). The centre of the fruit contains five carpels arranged star-like, each carpel containing one or two (rarely three) seeds.***********The wild ancestor of Malus domestica is Malus sieversii. It has no common name in English, but is known in Kazakhstan, where it is native, as 'alma'; in fact, the region where it is thought to originate is called Alma-Ata, or 'father of the apples'. This tree is still found wild in the mountains of Central Asia in southern Kazakhstan, Kyrgyzstan, Tajikistan, and Xinjiang, China. For many years, there was a debate about whether M. domestica evolved from chance hybridisation among various wild species. Recent DNA analysis by Barrie Juniper, Emeritus Fellow in the Department of Plant Sciences at Oxford University and others, has indicated, however, that the hybridisation theory is probably false. Instead, it appears that a single species still growing in the Ili Valley on the northern slopes of the Tien Shan mountains at the border of northwest China and the former Soviet Republic of Kazakhstan is the progenitor of the apples we eat today. Leaves taken from trees in this area were analysed for DNA composition, which showed them all to belong to the species M. sieversii, with some genetic sequences common to M. domestica.*****************There are more than 7,500 known cultivars of apples. Different cultivars are available for temperate and subtropical climates. Reputedly the world's biggest collection of apple cultivars is housed at the National Fruit Collection in England. Apples do not flower in tropical climates because they have a chilling requirement. ************************ Commercially popular apple cultivars are soft but crisp. Other desired qualities in modern commercial apple breeding are a colourful skin, absence of russeting, ease of shipping, lengthy storage ability, high yields, disease resistance, typical 'Red Delicious' apple shape, long stem (to allow pesticides to penetrate the top of the fruit), and popular flavour. *********************** Old cultivars are often oddly shaped, russeted, and have a variety of textures and colours. Many of them have excellent flavour (often better than most modern cultivars), but may have other problems which make them commercially unviable, such as low yield, liability to disease, or poor tolerance for storage or transport. A few old cultivars are still produced on a large scale, but many have been kept alive by home gardeners and farmers that sell directly to local markets. Many unusual and locally important cultivars with their own unique taste and appearance are out there to discover; apple conservation campaigns have sprung up around the world to preserve such local cultivars from extinction. In the United Kingdom old cultivars such as Cox's Orange Pippin and Egremont Russett are still commercially important even though by modern standards they are low yielding and disease prone. *************************** Although most cultivars are bred for eating fresh (dessert apples), some are cultivated specifically for cooking (cooking apples) or producing cider. Cider apples are typically too tart and astringent to eat fresh, but they give the beverage a rich flavour that dessert apples cannot. ***************************** Modern apples are, as a rule, sweeter than older cultivars. Most North Americans and Europeans favour sweet, subacid apples, but tart apples have a strong minority following. Extremely sweet apples with barely any acid flavour are popular in Asia and especially India. ***************************** Tastes in apples vary from one person to another and change continually over time. As an example, the U.S. state of Washington made its reputation for apple growing on Red Delicious. In recent years, many apple connoisseurs have come to regard the Red Delicious as inferior to cultivars such as Fuji and Gala due to its merely mild flavour and insufficiently firm texture.*****************Like most perennial fruits, apples are ordinarily propagated asexually by grafting. Seedling apples are different from their parents, sometimes radically. Most new apple cultivars originate as seedlings, which either arise by chance or are bred by deliberately crossing cultivars with promising characteristics. The words 'seedling', 'pippin', and 'kernel' in the name of an apple cultivar suggest that it originated as a seedling. Apples can also form bud sports (mutations on a single branch). Some bud sports turn out to be improved strains of the parent cultivar. Some differ sufficiently from the parent tree to be considered new cultivars. ********************** Some breeders have crossed ordinary apples with crabapples or unusually hardy apples in order to produce hardier cultivars. For example, the Excelsior Experiment Station of the University of Minnesota has, since the 1930s, introduced a steady progression of important hardy apples that are widely grown, both commercially and by backyard orchardists, throughout Minnesota and Wisconsin. Its most important introductions have included 'Haralson' (which is the most widely cultivated apple in Minnesota), 'Wealthy', 'Honeygold', and 'Honeycrisp'.****************Apple orchards are established by planting trees two to four year old. These small trees are usually purchased from a nursery where they are produced by grafting or budding. First, a rootstock is produced either as a seedling or cloned using tissue culture or layering. This is allowed to grow for a year. Then, a small section of branch called a scion is obtained from a mature apple tree of the desired cultivar. The upper stem and branches of the rootstock are cut away and replaced with the scion. In time, the two sections grow together and produce a healthy tree. *************************** Rootstocks affect the ultimate size of the tree. While many rootstocks are available to commercial growers, those sold to homeowners who want just a few trees are usually one of two cultivars; a standard seedling rootstock that gives a full-size tree, or a semi-dwarf rootstock that produces a somewhat smaller tree. Dwarf rootstocks are generally more susceptible to damage from wind and cold. Full dwarf trees are often supported of posts or trellises and planted in high density orchards which are much simpler to culture and greatly increase productivity per unit of land.