There are 34 species of crabapple tree in the Malus genus, not including Malus domestica, the common apple tree and their combined 700 cultivated subspecies. Both crabapples and regular apples are members of the rose family. Their sole distinction from one another is the size of their fruit. It is considered a crabapple if the fruit is smaller than 2 inches in diameter. To that end, the species of crabapple trees are just as diverse as regular apples.
Though one species of crabapple can be transplanted to the locale of another species with no adverse effects, crabapple species are categorized based on their habitat of origin. Asian species include the Japanese, Chinese and Asian wild, respectively known as Malus floribunda, Malus hupehensis and Malus sieversii. European species include the Florentine crabapple, Malus florentina; the European wild crabapple, Malus sylvestris; and sargent's apple, Malus sargenti. North American species include the shrub apple, Pacific crabapple and midget crabapple, known as Malus brevipes, Malus fusca and Malus micromalus.
Crabapples inhabit the temperate zones of North America, Europe and Asia. They are particularly abundant in areas with rich, loamy soils. As they produce tap roots which burrow down for yards, crabapples have little need for irrigation or excessive rainfall, hence they do not live in areas with high water tables, poorly draining soil or high annual rainfalls.
All crabapples have dense, woody foliage and the characteristic dome apple tree shape. Leaves range between 1.2 and 3.9 inches in length with a vein structure tangential to the leaf's spine, smooth edges and angular points. Flowers have five petals, except for Asian varieties which can have between four and eight petals, and appear in loose clusters called corymbs. Colors are various shades of white, pink or red. Fruit are globular, waxy, with most species being deep red. 'Golden Hornet' and similar cultivars are yellow, but they are the minority.
Authors Gerald Jonas, Bonnie Kreitler, Ann Reilly and David S. Thomson write in their book "Perennials" that the prairie crabapple, Malus ioensis, is the largest species of crabapple at an average of 50 feet in height when mature. Likewise, the midget crabapple, Malus micromalus, is the smallest at 4 feet high. Botanist John L. Fiala confirms this in his 2003 work "Flowering Crabapples: The Genus Malus."
It's commonly believed that crabapple trees' fruits are inedible or even poisonous. This is not true. All species of crabapple tree produce edible fruit, though some, like the Siberian crabapple, are very sour and require preparation and/or sweetening to be palatable.
Most species of crabapple grow wild and are uncultivated. Because of this, their function is reduced to use as an intermittent fruit tree. Those cultivars with sweet fruit can be eaten raw or used in baking. The sour varieties are canned. The flowering crabapple, Malus hopa, is cultivated as a large ornamental tree because of its abundant blossoms in spring.