16. Malus Mill. (apple)

Plants shrubs or small to medium trees. Branches sometimes producing short, stout branchlets with thorny tips, these indeterminate, mostly eventually become elongated and leafy. Bark dark brown to gray, on younger trunks relatively smooth but with prominent, raised branch scars and lenticels, on older trunks sometimes developing a network of ridges, these breaking up into more or less rectangular, fine, scaly plates, sometimes peeling. Winter buds ovoid to more or less conic, with several overlapping scales. Leaves alternate but often appearing clustered at the tips of short branchlets, rolled or folded longitudinally during development, mostly long-petiolate, the petioles lacking glands. Stipules small, membranous to papery, shed early (sometimes larger, more herbaceous, and more persistent on rapidly growing vegetative shoots). Leaf blades simple, unlobed or shallowly, pinnately few-lobed, variously shaped, the margins bluntly to sharply toothed, the surfaces glabrous or hairy at maturity, the upper surface lacking glands. Inflorescences terminal on lateral short branchlets, dome-shaped, umbellate clusters (lacking a noticeable central axis) of 2–6 long-stalked flowers, produced as the leaves uncurl or later, the axis and stalks glabrous or hairy, the stalks each with a small bract at the base, this linear to narrowly oblong-elliptic, brown to reddish brown, shed early. Flowers epigynous, often fragrant, the hypanthium fused to the ovaries, cup-shaped to ellipsoid or more or less urn-shaped, relatively open at the tip, glabrous or hairy. Sepals 5, spreading to somewhat reflexed at flowering, lanceolate, angled or tapered to a sharply pointed tip, the margins and/or upper surface hairy, sometimes persistent at fruiting. Petals 5 (except in rare doubled forms), broadly obovate to nearly circular, pink or pinkish white, in some species white at flowering but pinkish-tinged in bud, often fading to white with age. Stamens 15 to numerous, the anthers yellow or pink. Pistil 1 per flower, of 2–5 fused carpels. Ovary inferior, but sometimes protruding slightly from the hypanthium, with 2–5 locules, each with usually 2 ovules. Styles 2–5, fused toward the base, the fused portion densely hairy, protruding from the hypanthium the stigmas capitate or club-shaped. Fruits pomes, globose or nearly so, glabrous at maturity, variously colored, the surface not dotted, with 2–10 more or less easily exposed seeds embedded in the “core” of leathery to papery carpel wall remains and the fleshy portion, this lacking stone cells. Seeds obovoid to narrowly obovoid, the outer surface smooth, light brown to black. Twenty-five to 47 species, North America, Europe, Asia, introduced widely.

Steyermark (1963) and some other authors have classified Malus as a subgenus of a broadly defined Pyrus. For further discussion, see the treatment of that genus. Species limits among the apples and crab apples remain poorly understood.