FNA: Malus vs. Rosaceae tribe Maleae

Distribution

North America; Eurasia [Introduced widely, especially in temperate regions]

HI; North America; Mexico; Central America; Eurasia; Africa; Atlantic Islands (Madeira) [Introduced in temperate southern hemisphere]

Discussion

Species 25–55 (10 in the flora).

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Genera 29, species 550–840+ (18 genera, 270 species, including 18 hybrids, in the flora).

The family name Malaceae Small (1903) is a conserved name, with Malus as its type genus. In contrast, the family name Pyraceae Vest (1818), with Pyrus as its type, is not a conserved name. Although Maleae was published later than Pyreae (1869), a Rosaceae tribe that includes both Malus and Pyrus is to be called Maleae (see Melbourne Code, Article 19.5, Example 5).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key

1. Sepals deciduous in fruit	→ 2
1. Sepals persistent in fruit	→ 6
2. Leaves usually lobed	→ 3
2. Leaves unlobed	→ 4
3. Styles glabrous; pomes yellow to purplish red, oblong, sometimes ovoid or obovoid.	M. fusca
3. Styles proximally villous or lanate; pomes red or brownish yellow, subglobose.	M. toringo
4. Sepals lanceolate, longer than tube; anthers yellow before dehiscence.	M. baccata
4. Sepals triangular-ovate, equal to or shorter than tube; anthers white before dehiscence	→ 5
5. Leaves obtusely serrulate; sepal apices obtuse; petals usually more than 5; styles 4 or 5; pomes pyriform or obovoid.	M. halliana
5. Leaves sharply serrulate; sepal apices acute or acuminate; petals 5; styles 3(or 4); pomes ellipsoid or subglobose.	M. hupehensis
6. Cores of pomes enclosed at apex, sclereids absent or sparse surrounding core; anthers yellow before dehiscence; leaf blades of vigorous shoots unlobed	→ 7
6. Cores of pomes not enclosed at apex, sclereids abundant surrounding core; anthers rose, pink, salmon, or purple before dehiscence; leaf blades of vigorous shoots often lobed	→ 8
7. Leaf margins obtusely serrate, sometimes serrate-crenate; pomes globose or depressed-globose, sepals not swollen at base (cultivated apple).	M. pumila
7. Leaf margins acutely serrate or serrulate, sometimes doubly serrate; pomes ovoid or oblong, sepals swollen at base.	M. prunifolia
8. Sepals hoary-tomentose; leaves abaxially tomentose.	M. ioensis
8. Sepals abaxially glabrous, sometimes glabrescent; leaves abaxially glabrous (villous only on veins)	→ 9
9. Flowering shoot leaves usually elliptic or oblong, bases usually cuneate, margins crenate, crenate-serrate, or entire, apices rounded (with point or acute).	M. angustifolia
9. Flowering shoot leaves usually ovate, triangular-ovate, or lanceolate, bases usually rounded or cordate, margins usually serrate, apices acute or broadly acute (rounded with point or rounded).	M. coronaria

1. Leaf margins usually horny; carpels free; flowers: perianth and androecium perigynous; fruits woody capsules surrounded by a hypanthium, splitting into 5 follicles; seeds winged	Vauquelinia
1. Leaf margins not horny; carpels ± adnate to hypanthium; flowers: perianth and androecium epigynous; fruits pomes; seeds not winged or pyrenes.	→ 2
2. Fruiting carpels woody or bony.	→ 3
3. Leaf margins entire; stipules short-adnate to petiole; stems unarmed; sepals erect in flower; petal base clawed.	Cotoneaster
3. Leaf margins ± serrate, crenate, serrulate, or crenulate, sometimes entire; stipules free; stems usually armed (sometimes with compound thorns), sometimes unarmed; sepals spreading in flower; petal base slightly or barely clawed.	→ 4
4. Leaves persistent or late-deciduous; flowers 3–10(–12) mm diam., hypanthium campanulate; pomes 3–8 mm diam.	Pyracantha
4. Leaves deciduous (sometimes winter-persistent in south); flowers 8–35 mm diam., hypanthium ± obconic; pomes 6–40 mm diam.	→ 5
5. Flowers 8–25 mm diam., stamens 5–20 (rarely 30–45); pomes yellow to red or purplish to black mature, 6–20(–25) mm diam.; pyrenes 1–5; short shoots present; inflorescences 1–50-flowered, domed panicles, corymbose, or flowers solitary.	Crataegus
5. Flowers 25–35 mm diam., stamens 25–35(–40); pomes brownish, 15–40 mm diam.; pyrenes 5; short shoots rare or absent; inflorescences 1(or 2) flowered	Mespilus
2. Fruiting carpels cartilaginous.	→ 6
6. Stems armed (thorns present).>	→ 7
7. Stipules persistent; pedicels short or absent; styles basally connate 1/3 of length; pome flesh without stones; stamens 40–60; fruiting sepals deciduous.	Chaenomeles
7. Stipules usually deciduous or caducous; pedicels present; styles distinct or basally connate; pome flesh with stones (at least near carpels and epidermis); stamens 15–50; fruiting sepals persistent or deciduous.	→ 8
8. Pome flesh with stone cells adjacent to carpels and epidermis; styles basally connate.	Malus
8. Pome flesh with abundant stone or grit cells; styles distinct.	Pyrus
6. Stems unarmed.	→ 9
9. Inflorescences: flowers solitary or 1–5-flowered, corymbs or cymes.	→ 10
10. Pomes yellow; ovules (seeds) many; inflorescences: flowers solitary.	→ 11
11. Leaf margins entire, abaxial surfaces densely villous; buds ovoid, apices obtuse or acuminate, tomentose; young branches tomentose, glabrescent; stipules caducous; flowers 40–50 mm diam., petals white or light pink, suborbiculate, ovate, or obovate, stamens equal to or slightly longer than petals; pomes pyriform or subglobose, 30–50 mm.	Cydonia
10. Pomes pink, yellow-orange, purple, purplish or bluish black, brownish, or nearly black; ovules (seeds) (1 or)2; inflorescences 1–5-flowered, cymes or corymbs.	→ 12
12. Pomes yellow-orange; stipules adnate to petiole and base of blade; petioles short or absent; leaf blades elliptic to oblanceolate or linear.	Peraphyllum
12. Pomes pink, bluish or purplish black, purple, brownish, or nearly black; stipules free; petioles present; leaf blades elliptic, elliptic-oblong, or oblong-ovate to orbiculate.	→ 13
13. Leaves leathery, drought-deciduous or persistent; sepals nearly orbiculate (inner broadly deltate), petals round or kidney-shaped; carpels barely connate or distinct, styles lateral; pomes translucent, vivid pink, drying purplish black.	Malacomeles
13. Leaves membranous to coriaceous (not leathery), deciduous; sepals triangular to lanceolate, petals linear to orbiculate; carpels connate, styles terminal; pomes bluish or purplish to nearly black, pinkish or maroon-purple, dark purple-blue, or brownish.	Amelanchier
9. Inflorescences (4 or)5–400+-flowered, panicles, sometimes racemes, corymbs, or subumbellate.	→ 14
14. Leaves persistent, leathery; carpels basally adnate to hypanthium.	→ 15
15. Leaf margins flat; flowers 15–20 mm diam.; pedicels short or nearly absent; hypanthia usually tomentose; stamens 20; carpels connate, styles (2–)5; pomes soft apricot yellow, 20–30 mm (diam.).	Eriobotrya
15. Leaf margins revolute; flowers 10 mm diam.; pedicels present; hypanthia glabrous or weakly floccose; stamens 10; carpels distinct, styles 2 or 3; pomes usually bright red, sometimes yellow, 5–10 mm	Heteromeles
14. Leaves usually deciduous, sometimes semipersistent or persistent (then margin entire), membranous to ± leathery; carpels adnate to all or 1/3–1/2 of hypanthium.	→ 16
16. Pome flesh with stones or sclereids.	→ 17
17. Inflorescences terminal, 6–400+-flowered flat-topped or rounded panicles; flowers opening after leaf expansion, 5–17 mm diam.; sepals erect or ascending; leaves pinnately divided, sometimes simple or lobed.	Sorbus
17. Inflorescences terminal on short shoots, 4–9-flowered racemes or simple corymbs, umbel-like; flowers developing with or before leaves, 15–45 mm diam.; sepals reflexed; leaves simple.	Pyrus
16. Pome flesh without stones.	→ 18
18. Stipules adnate to petiole, persistent	Aronia
18. Stipules free, caducous or deciduous.	→ 19
19. Leaves persistent or deciduous; inflorescences corymbose or subumbellate; pomes red or black.	Photinia
19. Leaves deciduous; inflorescences racemes; pomes bluish or purplish to nearly black, pinkish or maroon-purple, dark purple-blue, or brownish	Amelanchier