58. Malus Miller, Gard. Dict. Abr. ed. 4. vol. 2. 1754.
Apple, pommier [Latin malus, apple tree]
Elizabeth E. Dickson
Shrubs or trees, 2–200 dm. Stems 1+ (derived from root shoots), erect; bark dark brown, reddish brown, or gray, ˂firm, platy or scaly˃; long and short shoots present; thorns present (modified short shoots); glabrous, glabrescent, villous, densely puberulent, or tomentose. Leaves deciduous [semipersistent], cauline, simple, ˂shoot dimorphism, long- and juvenile-shoot leaves usually larger and more deeply serrate (lobed) than short-shoot leaves˃; stipules deciduous (or persistent on vigorous shoot leaves in M. baccata), basally adnate to petiole, linear-lanceolate to lanceolate, sometimes filiform, ˂membranous, sometimes herbaceous˃, margins entire, serrulate, glandular-serrate, sparsely glandular-denticulate, or white-ciliate; petiole present; blade elliptic, ovate, obovate, triangular-ovate, oval, lanceolate, ovate-oblong, or oblong, (2–)4–12 cm, membranous or leathery, margins flat, sometimes lobed, dentate, serrulate, serrate, doubly serrate, crenate, or sometimes entire, venation pinnate (craspedodromous when lobed, camptodromous when unlobed), surfaces glabrous or tomentose. Inflorescences terminal ˂on short shoots˃, 2–12-flowered, ˂flat-topped˃ panicles, glabrous or tomentose; bracts present (absent in M. fusca), ˂caducous, ovate, linear-lanceolate, membranous, glabrous˃; bracteoles present. Pedicels present. Flowers bisexual (occasionally andromonoecious in M. halliana), opening with leaves, perianth and androecium epigynous, 15–50 mm diam.; hypanthium campanulate, size not recorded, glabrous or tomentose; sepals 5, reflexed to wide spreading, triangular, triangular-lanceolate, triangular-ovate, or lanceolate; petals 5 (or more in M. halliana), white, pink, or red, suborbiculate, obovate, narrowly or oblong-obovate, ovate, or ± elliptic, ˂base clawed˃; stamens 15–50, ˂unequal˃, usually shorter than, rarely equal to, petals; carpels 3–5, connate, adnate to hypanthium, styles ˂3–5˃, emerge from base of hypanthium, basally connate, ˂glabrous or tomentose basally˃; ovules 2. Fruits pomes, green, yellow, or red, globose, depressed-globose, obovoid, or oblong, 6–50(–70) mm diam., ˂glaucous, waxy˃, punctate; ˂flesh homogeneous, stone cells adjacent to carpels and epidermis˃; hypanthium persistent; sepals persistent or deciduous, erect or reflexed; carpels cartilaginous; styles persistent or deciduous. Seeds 2 per carpel, ˂light, dark, or reddish brown, smooth˃. x = 17.
Species 25–55 (10 in the flora): North America, Eurasia; introduced widely, especially in temperate regions.
Malus has great economic value; species are widely cultivated throughout the world for their edible fruit (not all species), ornamental fruit, or flowers. Mammals and birds eat cultivated and wild apples, which can result in the spread of seed and naturalization of species. The hard wood is occasionally used to make furniture and tools, and as fuel. The apple has symbolic significance in western cultures, including Greek, Roman, and Judeo-Christian mythologies. The apple often represents desire, temptation, and sin in art and literature (malum is Latin for evil), symbolizing sexuality, love, and the forbidden fruit of the Garden of Eden.
Cross-compatibility among species is common. Hybridization can occur naturally in botanical gardens and in the wild, or artificially through breeding. Polyploid forms and asexual seed production (apomixis) occur in some species.
The taxonomy of Malus has been revised at least three times, with some authors placing species within the genus Pyrus. Recent morphologic work has suggested that Malus be retained as a separate genus based on fully adnate carpels and deeply inferior ovaries (K. R. Robertson et al. 1991), with molecular evidence providing support (C. S. Campbell et al. 1995). Cultivation, hybridization, and introgression have led to hundreds of species names within Malus. The genus requires a comprehensive worldwide revision.
The eastern North American apples stand apart from other members of the genus by having unique floral and fruit traits, which define sect. Chloromeles (Decaisne) Rehder. Although distinctive morphologic extremes are obvious, continuous variation within this overall homogeneous group blurs species boundaries. Historically, taxonomic confusion has resulted from names being applied to slight variations in: leaf lobing and serration; patterns of leaf venation; leaf, calyx, and pedicel indument; and fruit shape. Leaves of vigorous long shoots often differ in shape and hairiness from those of short flowering shoots on the same tree. Polyploidy and apomixis may contribute to taxonomic difficulties by locking suites of traits together into morphologic forms. Morphologic patterns within the group can shift. Studies indicate that diploids within natural populations occasionally produce triploid and tetraploid progeny; triploids can give rise to tetraploids (E. E. Dickson 1995). Preliminary genetic studies do not clarify species boundaries and suggest a single monotypic species, Malus coronaria (Dickson et al. 1991; Dickson 1995). This treatment takes a conservative approach by recognizing three morphologic extremes as species. Further work is warranted to clarify the taxonomy of sect. Chloromeles.
The description of Malus prunifolia is based on Y. Asami (1927) and Gu C. Z. and S. A. Spongberg (2003); M. baccata and M. halliana are based on Gu and Spongberg; M. hupehensis is based on Gu and Spongberg and C. A. Huckins 1972; and M. toringo (as M. sieboldii) is based on Asami, Huckins, and Gu and Spongberg.
Selected references Dickson, E. E. 1995. Systematic Studies of Malus sect. Chloromeles. Ph.D. dissertation. Cornell University. Dickson, E. E., S. Kresovich, and N. F. Weeden. 1991. Isozymes in North American Malus (Rosaceae): Hybridization and species differentiation. Syst. Bot. 16: 363–375. Huckins, C. A. 1972. A Revision of the Sections of the Genus Malus Miller. Ph.D. dissertation. Cornell University.