Apple trees are typically 4–12 metres (13–39 feet) tall at maturity, with a dense, twiggy crown. Theleaves are 3–10 centimetres (1+1⁄4–4 inches) long, alternate, simple, with a serrated margin. Theflowers are borne incorymbs, and have fivepetals, which may be white, pink, or red, and areperfect, with usually red stamens that produce copiouspollen, and ahalf-inferior ovary; flowering occurs in the spring after 50–80growing degree days (varying greatly according to subspecies andcultivar).[citation needed]
Many apples requirecross-pollination between individuals byinsects (typicallybees, which freely visit the flowers for bothnectar andpollen); these are called self-sterile, so self-pollination is impossible, making pollinating insects essential.[5]
A number of cultivars are self-pollinating, such as 'Granny Smith' and 'Golden Delicious', but are considerably fewer in number compared to their cross-pollination dependent counterparts.[citation needed]SeveralMalus species, including domestic apples,hybridize freely.[6]
Thefruit is a globosepome, varying in size from1–4 cm (1⁄2–1+1⁄2 in) in diameter in most of the wild species, to6 cm (2+1⁄4 in) inM. sylvestris sieversii, 8 cm (3 in) inM. domestica, and even larger in certain cultivated orchard apples. The centre of the fruit contains fivecarpels arranged star-like, each containing one or twoseeds.[citation needed]
36 species and 4 hybrids are accepted.[2] The genusMalus is subdivided into eight sections (six, with two added in 2006 and 2008).[citation needed] The oldest fossils of the genus date to theEocene (Lutetian), which are leaves belonging to the speciesMalus collardii andMalus kingiensis from western North America (Idaho) and theRussian Far East (Kamchatka), respectively.[7]
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 asrootstocks for domestic apples to add beneficial characteristics.[8] For example, the rootstocks ofMalus baccata varieties are used to give additional cold hardiness to the combined plants for orchards in cold northern areas.[9]
They are also used aspollinizers in appleorchards. Varieties of crabapple 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 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 inbonsai culture.[10][11][12]
Ripe apples (M. domestica)Baskets of crab apples for sale in Connecticut in 1939
Crabapple fruit is not an importantcrop in most areas, being extremelysour due tomalic acid (which like the genus derives from the Latin namemālum), and in some species woody, so is rarely eaten raw. In someSoutheast Asian cultures, they are valued as a sourcondiment, sometimes eaten with salt andchilli orshrimp paste.[citation needed]
Some crabapple varieties are an exception to the reputation of being sour, and can be very sweet, such as the 'Chestnut' cultivar.[23]
Crabapples are an excellent source ofpectin. Using sugar and spices such as ginger, nutmeg, cinnamon, and allspice, theirjuice can be made into ruby-coloured crab applejelly with a full, spicy flavour.[24] A small percentage of crabapples incider makes a more interesting flavour.[25] AsOld EnglishWergulu, the crab apple is one of the nine plants invoked in thepagan Anglo-SaxonNine Herbs Charm, recorded in the 10th century.
Applewood gives off a pleasant scent when burned, and smoke from an applewood fire gives an excellent flavour tosmoked foods.[26] It is easier to cut when green; dry applewood is exceedingly difficult to carve by hand.[26] It is a good wood for cooking fires because it burns hot and slow, without producing much flame.[26] Applewood is used to make handles ofhand saws; in the early 1900s 2,000,000 board feet of applewood were used annually for this purpose.[27]
^Phipps, James B.; Robertson, Kenneth R.; Smith, Paul G.; Rohrer, Joseph R. (1990). "A checklist of the subfamily Maloideae (Rosaceae)".Can. J. Bot.68 (10):2209–2269.doi:10.1139/b90-288.
^Rombauer, I.; Becker, M. R.; Becker, E. (2002) [2002].All About Canning & Preserving (The Joy of Cooking series). New York: Scribner. p. 72.ISBN0-7432-1502-8.
