Corymbs of 3-10 flowers are produced near the axils of the leaves on short spur-shoots. The flowers are pinkish in bud, but become white when they bloom. Each flower is 1½-2" across, consisting of 5 white petals, 5 light green sepals that are joined together at the base, about 20 stamens with pale yellow anthers, 4-5 styles, and an inferior ovary. The sepals are about 1/3" (8 mm.) in length, lanceolate-triangular in shape, and short-pubescent along their outer surfaces. After the blooming period, withered remnants of the sepals persist on each pome. The floppy pedicels are ¾-2" long, light green to pale red, and sparsely short-pubescent to nearly glabrous. The blooming period occurs during mid- to late-spring for about 2 weeks. Afterwards, the flowers are replaced by fruits that are referred to as 'pomes.' At maturity during late summer or autumn, these pomes are ¾-1" across, more or less globoid in shape, glabrous, and usually bright red (or less often yellow). Each pome has a slight depression where it is joined by the petiole, while its opposite end near the withered sepals has either a slight depression or such a depression is lacking (often the latter). The interior of the pome contains firm white flesh and about 8-10 seeds. No vegetative offsets are produced from the woody root system; this crab apple reproduces by reseeding itself.
Cultivation: Plum-Leaved Crab Apple adapts to full or partial sun, moist to dry-mesic conditions, and a variety of soil types, including loam, clay-loam, silty loam, and sandy loam. It is vulnerable to a variety of disease organisms that can affect the leaves or fruit.
Range & Habitat: The introduced Plum-Leaved Crab Apple has naturalized in Kane County and Champaign County (see Distribution Map). This species has rarely escaped from cultivation in Illinois, although available records may underestimate its occurrence. Plum-Leaved Crab Apple is native to parts of East Asia, including northern China. Typical habitats include overgrown shrubby areas, riverbanks, and fence rows. While this species is rarely cultivated anymore in its original form, it is still used as grafting stock for various apple cultivars.
Faunal Associations: Crab apples (Malus spp.) attract a variety of wildlife. Their flowers are cross-pollinated primarily by bees, including Andrenid bees (Andrena spp.), honeybees, and bumblebees. Both nectar and pollen are available as floral rewards. The larvae of some beetles bore through the wood of crab apples; they include Agrilus vittaticollis (Flat-Headed Apple Tree Borer), Saperda candida (Round-Headed Apple Tree Borer), and Amphicerus bicaudatus (Apple Twig Borer). Other insects suck juices from the leaves, young shoots, inner bark, or roots; they include Aphis pomi (Green Apple Aphid), Dysaphis plantaginea (Rosy Apple Aphid), Eriosoma lanigera (Woolly Apple Aphid), Typhlocyba pomaria (White Apple Leafhopper), Ceresa bubalus (Buffalo Treehopper), and Lepidosaphes ulmi (Oystershell Scale). The white larvae of a fruit fly, Rhagoletis pomenella (Apple Maggot), develop in the fruit of crab apples. Other insect feeders include the caterpillars of such moths as Balsa malana (Many-Dotted Appleworm), Malacosoma americanum (Eastern Tent Caterpillar), Phyllonorycter crataegella (Apple Blotch Leaf-Miner), and Cydia pomonella (Codling Moth); the Moth Table has a more complete list of these species.
In addition, caterpillars of the butterflies Limenitis arthemis astyanax (Red-Spotted Purple) and Papilio glaucus (Tiger Swallowtail) occasionally feed on the leaves. Vertebrate animals use crab apple trees as a source of shelter and food. The fruit is eaten by such mammals as the Black Bear, Red Fox, Gray Fox, Coyote, Opossum, Raccoon, Gray Squirrel, Fox Squirrel, Striped Skunk, Deer Mouse, and Pine Mouse. White-Tailed Deer browse on the leafy twigs and the Cottontail Rabbit gnaws on the bark of saplings (Barnes, 1999; Martin et al., 1952/1962). Although the fruits of Plum-Leaved Crab Apple are somewhat large to be carried about by birds, they are still pecked at and occasionally eaten by various upland gamebirds and songbirds (see Bird Table). Because of the dense branching structure of these shrubs or small trees, they provide good nesting habitat for the Song Sparrow, Orchard Oriole, Yellow-Breasted Chat, and other songbirds.
Photographic Location: A shrubby area of Busey Woods in Urbana, Illinois.
Comments: Because so many cultivars of crab apples (Malus spp.) are grown as ornamental shrubs or trees, naturalized specimens of crab apples are often difficult to identify as some hybridization across different species is common. Plum-Leaved Crab Apple can be identified by its relatively robust size, the characteristics of its leaves, and the characteristics of its fruits. For example, the leaves of Plum-Leaved Crab Apple are more hairy than those of Siberian Crab Apple (Malus baccata) and less hairy than those of the cultivated Apple (Malus pumila). Its leaves also lack the lobes that are common on the leaves of native crab apples in Illinois (Malus coronaria & Malus ioensis). The fruits of Plum-Leaved Crab Apple are larger in size than those of Siberian Crab Apple, but they are smaller in size than those of the cultivated Apple. While the fruits of Plum-Leaved Crab Apple are usually red, the fruits of native crab apples in Illinois are usually greenish yellow. Because of its intermediate characteristics, some authorities have proposed that Plum-Leaved Crab Apple may be a naturally occurring hybrid between the Siberian Crab Apple and the cultivated Apple. However, it is currently classified as a distinct species in most taxonomies.