Malus, the apples, includes about 30-35 species of small deciduous trees or shrubs in the family Rosaceae, including both wild and domesticated varieties of apples. Non-edible forms of the tree are called "wild apples," "crab apples," "crabapples," or "crabs," this name being derived from their small and sour, unpalatable fruit. The genus is native to the temperate zone of the Northern Hemisphere, in Europe, Asia and North America.
Apple trees are relatively small, typically less than 20 feet tall at maturity, with a dense, twiggy crown. The flowers are borne in corymbs, and have five petals, which may be white, pink or red, typically with red stamens that produce copious pollen. Flowering occurs in the spring after 50-80 days of sufficient warmth. Apples require cross-pollination between individuals by insects (typically bees, which freely visit the flowers, for both nectar and pollen); all are self-sterile. The honeybee is the most effective pollinator of apples. Malus species are used as food plants by the larvae of a large number of Lepidoptera, attracting a number of brightly colored butterflies and moths.
Crabapple fruit are mostly red, but some cultivars produce yellow fruits. Crabapple trees are commonly grown as ornamental trees, prized for their beautiful flowers or fruit, with numerous cultivars bred for these qualities and for resistance to disease. Crabapples are also used in agriculture to aid in the production of edible apples.