Prunus
Sp. Pl. 1: 473. 1753.
Gen. Pl. ed. 5, 213. 1754.
Shrubs or trees, sometimes forming clonal thickets, 1–400 dm, glabrous or hairy. Stems 1–20+; bark reddish, reddish-brown, gray-brown, or dark gray; long and short-shoots usually present; thorns present or absent. Leaves deciduous or persistent, cauline; stipules caducous, linear to lanceolate, margins toothed to lobed, usually glandular; petiole present or absent, usually glandular near blade; blade elliptic, oblong, suborbiculate, ovate, lanceolate, linear, obovate, oblanceolate, spatulate, fan-shaped, or rhombic, seldom folded along midribs, 0.5–18 cm, membranous to leathery, margins flat, usually entire or toothed, sometimes undulate, teeth usually glandular, sometimes eglandular. Inflorescences terminal on short-shoots or from axils of previous year’s leaves, 1–64 (–90) [–100] -flowered, racemes, corymbs, umbellate fascicles, 2-flowered fascicles, or solitary; bracts sometimes present; bracteoles present. Pedicels usually present, sometimes absent. Flowers usually bisexual, sometimes unisexual (then plants usually dioecious, sometimes andropolygamous), blooming before or at leaf emergence, 4–40 mm diam.; hypanthium 1.5–8 mm, exterior glabrous or hairy; sepals 5, erect to reflexed, usually triangular, semicircular, ovate, or oblong, rarely ovate-elliptic, lanceolate, or obovate; petals 5 (–50+ in doubled ornamentals), usually white to pink or dark-pink, sometimes yellowish, usually suborbiculate to elliptic or obovate, sometimes oblong, rarely ovate, oblanceolate, or rhombic, base usually clawed; stamens 10–30, usually shorter than or equal to petals, sometimes longer. Drupes 1, greenish yellow to yellowish or orange to bright or dark red, reddish-brown, or dark purple to black, globose to ovoid, ovoid-oblong, ellipsoid, or obovoid, 5–30 (–80) mm; hypanthium deciduous, rarely persistent in fruit; sepals falling with hypanthium; mesocarps usually fleshy, sometimes leathery to dry, rarely splitting along suture to reveal stone; endocarps forming globose to ovoid or ellipsoid to fusiform stones, sometimes flattened laterally. Seed 1. x = 8.
Distribution
North America, Mexico, Central America, South America, Eurasia, Africa, Australia, most abundant in north-temperate regions
Discussion
Species 200+ (44 in the flora).
Prunus is important economically; it includes almonds, apricots, cherries, nectarines, peaches, and plums. Most commercial species are of Old World origin; Native Americans made use of Prunus fruits, especially plums, long before the Eurasian species were introduced. North American Prunus was consumed fresh, dried, and prepared with meat to form pemmican. Even though native North American plums have never rivaled those of Eurasia for commercial significance, some species were sources for hundreds of named cultivars selected and developed by settlers, farmers, and horticulturists in the late nineteenth and early twentieth centuries (U. P. Hedrick 1911). Luther Burbank also made use of native plums in carrying out crosses with P. salicina Lindley that led to most of the commercial plum crop grown in California. Small-scale research into the commercial potential of native plums continues today (W. R. Okie 2001).
European and Asian species of Prunus have been introduced into North America for their ornamental beauty and are used in the landscape as specimen and accent trees, foundation shrubs, hedges, and screens. Their fleshy fruits are favorites of birds and other frugivores, which disperse the seeds widely. Some species escape cultivation and their seedlings appear nearby, especially in disturbed soil. Included in this treatment are introduced species that not only escape frequently but also have become naturalized in the flora area, reproducing on their own. The following species are cultivated in North America and have been reported as rarely escaped or persisting; they are excluded here because they do not yet appear to be naturalized in the flora area: P. fruticosa Pallas, P. mume Siebold & Zuccarini, and P. triloba Lindley.
The taxonomic history of Prunus is long and complicated, in part due to the economic value of its fruit crops and also the ease with which some species hybridize. Here, Prunus is circumscribed in its broad sense based on the argument that when viewed on a worldwide scale, the morphologic discontinuities among the segregate genera diminish and they overlap with one another (R. McVaugh 1951). Included here are species that other botanists, from Linnaean times to the present (for example, Wu Z. and P. H. Raven 2003, vol. 9), have placed in Amygdalus, Armeniaca, Cerasus, Lauro-cerasus, Padus, and Persica. Systems of subgeneric classification have been proposed by those treating Prunus in the broad sense; as K. R. Robertson (1974) concluded, no consensus was reached on how many subgenera or sections should be recognized, or which species should be placed in which taxa. The most widely followed system has been that of A. J. Rehder (1940), who recognized five subgenera: Amygdalus, Cerasus, Lauro-cerasus, Padus, and Prunophora [= Prunus]. Phylogenetic studies employing DNA sequences from chloroplast and nuclear genes (E. Bortiri et al. 2001, 2002; S. Lee and J. Wen 2001) have shown that the five subgenera accepted by Rehder and his placement of individual species within them are not supported. So far, an alternative infrageneric classification of Prunus that accounts for the majority of its species has yet to be proposed. Character reconstruction, or the mapping of morphological characters onto phylogenetic trees based in large part on molecular data, shows that there is considerable homoplasy in most of the characters previously used to delimit subgenera, sections, and species (J. Shaw and R. L. Small 2004; Bortiri et al. 2006). Few new morphological characters useful in writing a key to the clades resolved by molecular phylogenetics have emerged. Prunus is presented here without division into subgenera or sections.
At the species level, Prunus has been the object of the usual combining and splitting common among taxonomists with different philosophies and opinions. In particular, over-reliance on the indument of various vegetative and floral parts has led to the naming of numerous species and infraspecific taxa. Similarly, too much has been made of fruit color and palatability in naming taxa of Prunus. Fruits of some cherries and plums go through a progression of color changes as they mature. A typical series is green to red to purple to black. Often, an individual tree whose fruits would be nearly black when fully ripe has its fruits removed by birds when they are still red or purple. These same fruits, which may be highly astringent when red or purple, are often more palatable to humans when dark purple to black. In general, a conservative approach toward species circumscription is taken here, one that in many cases reflects current usage. Widespread hybridization among plums has made their taxonomy particularly troublesome. J. Shaw and R. L. Small (2005) have shown that chloroplast DNA data provide resolution for P. subcordata and P. texana, while the rest of the North American plums form three primary clades with little resolution within each clade and no resolution among them. Multiple accessions of most eastern species were scattered on more than one clade. Analysis of sequences from nuclear genes has not done much to resolve relationships among the plums (J. R. Rohrer et al. 2008). Surely, as more molecular and genetic data are analyzed and, more importantly, correlated with morphological data, circumscriptions will be redrawn and the number of North American plum species further reduced.
Measurements of leaf size are from leaves on both long and short shoots. The larger values, especially those in parentheses, are found only on long shoots, and exceptionally fast-growing long shoots may have leaves that occasionally exceed the dimensions given. In the majority of Prunus, a true terminal bud is formed at the end of each vegetative shoot. In subgenera Emplectocladus Torrey and Prunus, the apical meristem aborts and leaves a nib of stem tissue soon surpassed distally by an enlarged axillary bud that assumes the end bud position and role in continuing longitudinal growth of the shoot during the next growing season. Such axillary end buds are called false terminal buds, or the twigs are described as lacking terminal buds. For clarity, the descriptions state that twigs have either terminal end buds or axillary end buds. The lengths of racemes were measured from the base of the peduncle to the distal end of the rachis (= central axis of inflorescence). For racemes terminal on leafy shoots, the length was measured from the node of the most distal leaf not subtending a flower. The number of flowers per umbellate fascicle was counted as the number of flowers emerging from one bud, rather than from a node or spur. Reports of more than six flowers in an umbellate fascicle are probably the result of counting flowers from more than one bud. Fruit sizes given in the descriptions are for fresh fruits. As fruits dry, they shrink to little more than the size of the stone.
Selected References
None.
Lower Taxa
Key
| 1 | Inflorescences 12–64(–90)-flowered, racemes (central axis lengths 4–25 times pedicels) | > 2 |
| 1 | Inflorescences 1–12-flowered, umbellate fascicles, corymbs, or racemes (central axis lengths 0–3.5 times pedicels) | > 9 |
| 2 | Leaves deciduous; racemes leafy at bases | > 3 |
| 2 | Leaves persistent; racemes leafless at bases | > 5 |
| 3 | Leaf margins crenulate-serrulate to serrate, teeth incurved or appressed; lateral veins 15–30 per side, flush abaxially; sepal margins usually entire, rarely glandular-toothed; hypanthia persistent. | Prunus serotina |
| 3 | Leaf margins serrulate to serrate, teeth ascending to spreading; lateral veins 6–18 per side, raised abaxially; sepal margins usually toothed, erose; hypanthia deciduous (leaving discs at bases of drupes) | > 4 |
| 4 | Petals 2–5(–7) mm; sepals 0.7–1.4 mm (lengths equal to widths); stones ± smooth. | Prunus virginiana |
| 4 | Petals (5–)6–9 mm; sepals 1.2–2 mm (lengths greater than widths); stones rugulose. | Prunus padus |
| 5 | Leaf abaxial surfaces eglandular (if glands present, restricted to margins) | > 6 |
| 5 | Leaf abaxial surfaces glandular, glands 1–several, proximal, flat, circular to oval | > 7 |
| 6 | Racemes: central axes 30–80 mm; leaf margins spinose-dentate to spinose-serrulate or entire; drupes 12–25 mm. | Prunus ilicifolia |
| 6 | Racemes: central axes 100–280 mm; leaf margins crenate-dentate; drupes 8–12 mm. | Prunus lusitanica |
| 7 | Leaf apices acute to acuminate, apicula obtuse; flowering Nov–Jan. | Prunus myrtifolia |
| 7 | Leaf apices usually acute to short-acuminate, sometimes obtuse-apiculate, apicula acute; flowering Feb–May | > 8 |
| 8 | Racemes: central axes 13–30(–43) mm; petals 1–1.5 mm; leaf blade margins entire or spinose-serrate; drupes 9–12 mm. | Prunus caroliniana |
| 8 | Racemes: central axes (35–)55–130 mm; petals 3–5 mm; leaf blade margins remotely serrulate or nearly entire; drupes 13–17 mm. | Prunus laurocerasus |
| 9 | Specimens with leaves and fruits | > 10 |
| 9 | Specimens with flowers (with or without leaves) | > 50 |
| 10 | Drupes hairy | > 11 |
| 10 | Drupes glabrous | > 22 |
| 11 | Trees, 30–100 dm; drupes 25–80 mm | > 12 |
| 11 | Shrubs, 5–30 dm (–40 dm in P. fremontii, –60 dm in P. subcordata); drupes 7–25 mm | > 14 |
| 12 | Leaf blades broadly ovate to suborbiculate, abaxial surfaces with tufts of hairs in vein axils; stones not pitted. | Prunus armeniaca |
| 12 | Leaf blades lanceolate to oblong, abaxial surfaces glabrous; stones pitted | > 13 |
| 13 | Petioles 5–10(–15) mm, not winged; leaf blades (50–)70–150 mm, folded along midribs; drupe mesocarps fleshy. | Prunus persica |
| 13 | Petioles (8–)10–25 mm, usually winged distally; leaf blades 25–100 mm, not folded along midribs; drupe mesocarps leathery. | Prunus dulcis |
| 14 | Drupe mesocarps fleshy | > 15 |
| 14 | Drupe mesocarps leathery to dry | > 17 |
| 15 | Pedicels 5–15 mm; drupes 15–25 mm; petioles 4–18 mm, usually glandular distally. | Prunus subcordata |
| 15 | Pedicels 0–5 mm; drupes 8–15 mm; petioles 1–7 mm, eglandular | > 16 |
| 16 | Leaf blades 1.7–3.5(–4.7) cm wide, margins singly to doubly serrate, teeth acute, usually eglandular, sometimes glandular, glands spheric; drupes red, sparsely hairy. | Prunus tomentosa |
| 16 | Leaf blades 0.4–1.1 cm wide, margins dentate, teeth obtuse, glandular, glands discoid; drupes usually yellow to greenish yellow, sometimes tinged with red, velutinous. | Prunus texana |
| 17 | Leaf bases long-attenuate; blades linear, narrowly elliptic, obovate, oblanceolate, or spatulate, (lengths 2.2–10 times widths) | > 18 |
| 17 | Leaf bases cuneate, obtuse, rounded, truncate, or subcordate; blades elliptic, ovate, obovate, spatulate, suborbiculate, rhombic, or fan-shaped, (lengths 1–2.6 times widths) | > 19 |
| 18 | Pedicels 0–4 mm; blades 0.1–0.2(–0.4) cm wide, margins nearly entire or obscurely and remotely serrulate in distal 1/3. | Prunus fasciculata |
| 18 | Pedicels (1–)4–12 mm; blades 0.2–0.6 cm wide, margins serrulate (sometimes obscurely so). | Prunus andersonii |
| 19 | Twigs glabrous; pedicels 2–12 mm, glabrous. | Prunus fremontii |
| 19 | Twigs canescent or puberulent; pedicels 0–3 mm, puberulent | > 20 |
| 20 | Leaf blades rhombic, obovate, or fan-shaped, bases broadly obtuse or rounded to nearly truncate, margins serrate or dentate in distal 1/2. | Prunus havardii |
| 20 | Leaf blades elliptic, ovate, obovate, or spatulate, bases cuneate to obtuse, margins usually entire, sometimes irregularly serrulate (sometimes dentate on long shoots), or irregularly serrate | > 21 |
| 21 | Leaf blades and petioles glabrous. | Prunus minutiflora |
| 21 | Leaf blades and petioles hairy. | Prunus eremophila |
| 22 | Twigs with terminal end buds; plants not thorny; stones not or slightly flattened (without lateral edges) | > 23 |
| 22 | Twigs with axillary end buds; plants sometimes thorny; stones slightly to ± or strongly flattened (with lateral edges) | > 32 |
| 23 | Leaf blade margins toothed in distal 1/2–2/3. | Prunus pumila |
| 23 | Leaf blade margins toothed to base | > 24 |
| 24 | Leaf blade margins usually doubly, sometimes singly, serrate, teeth sharp to aristate | > 25 |
| 24 | Leaf blade margins singly or doubly crenulate-serrulate to crenate-serrate, teeth blunt | > 27 |
| 25 | Twigs, petioles, and leaf blades glabrous; leaf apices caudate. | Prunus speciosa |
| 25 | Twigs and petioles hairy, leaf blades hairy abaxially along midribs and veins; leaf apices acuminate | > 26 |
| 26 | Petioles 10–20 mm; leaf bases rounded; inflorescences corymbs. | Prunus yedoensis |
| 26 | Petioles 5–10 mm; leaf bases obtuse; inflorescences umbellate fascicles. | Prunus subhirtella |
| 27 | Leaf apices usually rounded to obtuse, rarely acute. | Prunus emarginata |
| 27 | Leaf apices abruptly acuminate, acuminate, or acute | > 28 |
| 28 | Twigs densely puberulent; leaf blades 1.9–4.5 cm (lengths 1–1.5 times widths). | Prunus mahaleb |
| 28 | Twigs glabrous; leaf blades (2.5–)4.5–14 cm (lengths 1.5–4.3 times widths) | > 29 |
| 29 | Petioles 1–6 mm; shrubs, 5–20 dm. | Prunus glandulosa |
| 29 | Petioles 7–40 mm; shrubs or trees, 20–200 dm | > 30 |
| 30 | Leaf blades lanceolate, oblong-lanceolate, or elliptic; drupes 6–10 mm. | Prunus pensylvanica |
| 30 | Leaf blades broadly elliptic, elliptic-obovate, oblong, ovate, or obovate; drupes 13–30 mm | > 31 |
| 31 | Leaf abaxial surfaces moderately hairy, especially along midribs and veins, blades (4–)7–14 cm; petioles (14–)20–40 mm, with 1–3 glands distally and/or glands on margins at bases of blades. | Prunus avium |
| 31 | Leaf abaxial surfaces glabrous or glabrate, blades 4.4–6(–8) cm; petioles 10–24 mm, usually eglandular, sometimes with marginal glands at bases of blades. | Prunus cerasus |
| 32 | Leaf blade margins: teeth sharp, usually eglandular, sometimes with glands (especially near bases of blades) | > 33 |
| 32 | Leaf blade margins: teeth blunt, usually glandular (glands sometimes deciduous, each leaving scar on tooth) | > 38 |
| 33 | Leaf blades: margins coarsely, doubly serrate, apices usually acuminate to abruptly acuminate, rarely acute; drupes 15–30 mm, stones strongly flattened | > 34 |
| 33 | Leaf blades: margins finely and usually singly, sometimes doubly, serrulate, sometimes doubly serrate, apices usually obtuse to acute, sometimes short-acuminate, rarely rounded; drupes 9–18 mm, stones slightly to ± flattened | > 36 |
| 34 | Leaf surfaces: abaxial glabrous or sparsely hairy along main veins; petioles usually hairy adaxially, rarely glabrous, usually eglandular, sometimes glandular distally. | Prunus americana |
| 34 | Leaf surfaces: abaxial moderately to densely hairy; petioles hairy on both surfaces, usually glandular distally (sometimes on margins at bases of blades) | > 35 |
| 35 | Shrubs or trees, suckering; twigs usually hairy, sometimes glabrous; leaf bases usually cuneate to obtuse, sometimes rounded, (blade lengths 1.9–2.6 times widths). | Prunus americana |
| 35 | Trees, rarely suckering; twigs usually glabrous, sometimes hairy; leaf bases usually obtuse to rounded, sometimes subcordate, (blade lengths 1.6–2.1 times widths). | Prunus mexicana |
| 36 | Twigs and pedicels usually glabrous, sometimes hairy; leaf apices usually acute, sometimes short-acuminate, (blade lengths 2–2.7 times widths); shrubs or trees, 10–60 dm; Michigan, Appalachian Mountains, se coastal plain and piedmont. | Prunus umbellata |
| 36 | Twigs and pedicels usually densely, sometimes hairy, glabrate; leaf apices usually acute to obtuse, rarely rounded, (blade lengths 1.6–2.1 times widths); shrubs, 3–25 dm; Atlantic seaboard or s Great Plains | > 37 |
| 37 | Leaf adaxial surfaces glabrous; Atlantic seaboard. | Prunus maritima |
| 37 | Leaf adaxial surfaces finely hairy; s Great Plains. | Prunus gracilis |
| 38 | Twigs hairy | > 39 |
| 38 | Twigs glabrous | > 44 |
| 39 | Leaf blades: largest 1–5(–6.5) cm, apices rounded to acute (if blades longer than 40 mm, apices obtuse or rounded) | > 40 |
| 39 | Leaf blades: largest 5–11 cm, apices usually acute to acuminate, sometimes obtuse (in P. domestica) | > 42 |
| 40 | Pedicels 5–15 mm; petioles 4–18 mm. | Prunus subcordata |
| 40 | Pedicels 0–5(–8) mm; petioles 3–7 mm | > 41 |
| 41 | Leaves: surfaces hairy (especially along midribs and veins), blades 10–22 mm wide; petioles hairy, eglandular; drupes bluish black, 10–15 mm. | Prunus spinosa |
| 41 | Leaves: surfaces glabrous, blades 4–13 mm wide; petioles usually hairy adaxially, sometimes with glands distally; drupes reddish, 12–25 mm. | Prunus geniculata |
| 42 | Leaf blades lanceolate to elliptic or ovate, (lengths 2–3 times widths), usually folded along midribs; drupes 10–18 mm. | Prunus murrayana |
| 42 | Leaf blades broadly elliptic, elliptic, or obovate, (lengths 1.5–2 times widths), not folded along midribs; drupes 15–35 mm | > 43 |
| 43 | Leaf blades (2.5–)4–7(–9) cm, apices usually acute to abruptly acuminate, sometimes obtuse. | Prunus domestica |
| 43 | Leaf blades (5–)7–11 cm, apices abruptly acuminate. | Prunus nigra |
| 44 | Leaf blades usually lanceolate, oblanceolate, oblong-lanceolate, or narrowly elliptic, sometimes elliptic or oblong-obovate, (lengths 2–3 times widths), apices acute to long-acuminate | > 45 |
| 44 | Leaf blades broadly elliptic to elliptic, ovate, oblong-ovate, obovate, or suborbiculate, (lengths 1.5–2 times widths), apices rounded, obtuse, acute, or abruptly acuminate | > 47 |
| 45 | Petioles usually eglandular, sometimes with 1–2 glands distally; leaf blades 0.8–2 cm wide, marginal teeth with conspicuous, reddish orange glands. | Prunus angustifolia |
| 45 | Petioles usually with 1–5 glands distally; leaf blades 1.5–5.5 cm wide, marginal teeth with inconspicuous, blackish glands | > 46 |
| 46 | Leaf blades folded along midribs; plants usually suckering. | Prunus rivularis |
| 46 | Leaf blades not folded along midribs; plants rarely suckering. | Prunus hortulana |
| 47 | Leaf blades (5–)7–11 cm, apices abruptly acuminate. | Prunus nigra |
| 47 | Leaf blades 2–7(–9) cm, apices usually acute, obtuse, or rounded, sometimes abruptly acuminate (in P. domestica) | > 48 |
| 48 | Leaf blades elliptic, oblong-ovate, or suborbiculate, bases rounded or subcordate, apices usually obtuse to rounded, rarely acute. | Prunus subcordata |
| 48 | Leaf blades ovate, elliptic, or obovate, bases cuneate to obtuse, apices acute, obtuse, or abruptly acuminate | > 49 |
| 49 | Leaves: abaxial surfaces hairy along midribs and veins; drupes purple-red to yellow. | Prunus cerasifera |
| 49 | Leaves: abaxial surfaces hairy (especially along veins); drupes blue-black (green, yellow, or red in cultivars). | Prunus domestica |
| 50 | Ovaries hairy (or flowers staminate and petals 2–6 mm) | > 51 |
| 50 | Ovaries glabrous (or flowers lacking stamens and carpels, and petals 7–12 mm) | > 63 |
| 51 | Ovaries sparsely hairy or glabrous proximally, villous distally | > 52 |
| 51 | Ovaries usually densely hairy | > 53 |
| 52 | Inflorescences (3–)6–12-flowered, corymbs or racemes; hypanthia obconic, 2.5–3 mm; sepal margins entire; petals 3–8 mm. | Prunus emarginata |
| 52 | Inflorescences usually solitary flowers, sometimes 2-flowered fascicles; hypanthia tubular, 3.5–6 mm; sepal margins serrate; petals 9–13 m. | Prunus tomentosa |
| 53 | Trees, 30–100 dm, not thorny; twigs glabrous; hypanthia 4–7 mm | > 54 |
| 53 | Shrubs, rarely trees (P. subcordata), (5–)10–40(–60) dm, sometimes thorny; twigs glabrous or hairy; hypanthia 1.5–4 mm | > 56 |
| 54 | Twigs with axillary end buds; sepals reflexed, margins remotely glandular-toothed, neither ciliate nor tomentose; petals 8–12 mm, white (pink in bud). | Prunus armeniaca |
| 54 | Twigs with terminal end buds; sepals erect-spreading to spreading, margins entire, ciliate or tomentose; petals 10–25 mm, dark pink or pink to nearly white | > 55 |
| 55 | Petals dark pink; sepals abaxially hairy, margins ciliate. | Prunus persica |
| 55 | Petals pink to nearly white; sepals abaxially glabrous, margins tomentose. | Prunus dulcis |
| 56 | Flowers unisexual; sepal margins entire | > 57 |
| 56 | Flowers bisexual; sepal margins glandular-toothed | > 60 |
| 57 | Leaf blades 0.1–0.2(–0.4) cm wide, oblanceolate to linear; petioles 0 mm. | Prunus fasciculata |
| 57 | Leaf blades 0.2–1(–2.1) cm wide, ovate, elliptic, obovate, spatulate, rhombic, or fan-shaped; petioles 0.5–6 mm | > 58 |
| 58 | Hypanthial exterior and sepal abaxial surfaces hairy; California. | Prunus eremophila |
| 58 | Hypanthial exterior and sepal abaxial surfaces glabrous or glabrate; Texas | > 59 |
| 59 | Leaf blades elliptic or obovate, margins usually entire, sometimes irregularly serrulate, surfaces glabrous. | Prunus minutiflora |
| 59 | Leaf blades rhombic, obovate, or fan-shaped, margins serrate or dentate in distal 1/2, surfaces puberulent. | Prunus havardii |
| 60 | Hypanthial exterior and sepal abaxial surfaces tomentose; emerging leaf blades tomentose; Texas. | Prunus texana |
| 60 | Hypanthial exterior and sepal abaxial surfaces glabrous or hairy; emerging leaf blades usually glabrous, sometimes puberulent; California, Nevada, Oregon | > 61 |
| 61 | Leaf blades narrowly elliptic, obovate, oblanceolate, or spatulate, bases long-attenuate; petals usually dark pink, sometimes nearly white. | Prunus andersonii |
| 61 | Leaf blades elliptic, ovate, oblong-ovate, or suborbiculate, bases obtuse, rounded, subcordate, or truncate; petals usually white, sometimes pinkish rose | > 62 |
| 62 | Emerging leaf surfaces glabrous; sepals erect-spreading. | Prunus fremontii |
| 62 | Emerging leaf surfaces hairy; sepals broadly spreading to reflexed. | Prunus subcordata |
| 63 | Inflorescences 2–12-flowered, racemes or corymbs (each with peduncle) | > 64 |
| 63 | Inflorescences 1–5(–8)-flowered, umbellate fascicles or solitary flowers | > 68 |
| 64 | Hypanthia 4–8 mm (lengths greater than diams.); sepals 3–8 mm | > 65 |
| 64 | Hypanthia 1.8–3 mm (lengths ± equal to diams.); sepals 1.2–2.8 mm | > 66 |
| 65 | Pedicels glabrous or sparsely hairy; hypanthia and sepals glabrous; sepal margins entire or toothed, eglandular; plants blooming at leaf emergence. | Prunus speciosa |
| 65 | Pedicels, hypanthia, and sepals hairy; sepal margins glandular-toothed; plants blooming before leaf emergence. | Prunus yedoensis |
| 66 | Pedicels (8–)10–30 mm (subtended by minute bracts); central axes 0–8(–24) mm, (pedicels longer than central axes). | Prunus pensylvanica |
| 66 | Pedicels 3–18 mm (subtended by leafy bracts); central axes (5–)8–40 mm, (pedicels shorter than or equal to central axes) | > 67 |
| 67 | Leaves: apices abruptly acuminate, bases usually rounded to truncate, sometimes subcordate; twigs densely puberulent. | Prunus mahaleb |
| 67 | Leaves: apices usually rounded to obtuse, rarely acute, bases cuneate; twigs glabrous or hairy. | Prunus emarginata |
| 68 | Sepals entire or teeth eglandular | > 69 |
| 68 | Sepals glandular-toothed | > 81 |
| 69 | Petals 2 mm; pedicels 0–3 mm. | Prunus geniculata |
| 69 | Petals 3–15 mm; pedicels 3–52 mm | > 70 |
| 70 | Sepals oblong, glabrous; twigs with terminal end buds; plants not thorny | > 71 |
| 70 | Sepals lanceolate to oblong-ovate, ovate, or obovate, hairy (especially proximally on adaxial surfaces); twigs with axillary end buds; plants usually thorny | > 72 |
| 71 | Petals 4–7 mm; hypanthia 1.8–3 mm. | Prunus pensylvanica |
| 71 | Petals 12–15 mm; hypanthia 5–7 mm. | Prunus avium |
| 72 | Sepals 2.2–4(–5) mm; hypanthia 2–3.5 mm (sepals longer than hypanthia). | Prunus subcordata |
| 72 | Sepals 1–6 mm; hypanthia 1.5–7 mm (sepals equal to or shorter than hypanthia) | > 73 |
| 73 | Sepals broadly spreading to reflexed; petals 5–14 mm | > 74 |
| 73 | Sepals erect to spreading; petals 3–8 mm | > 77 |
| 74 | Inflorescences usually solitary flowers, sometimes 2-flowered fascicles; emerging leaves: marginal teeth glandular. | Prunus cerasifera |
| 74 | Inflorescences 2–5-flowered (at least some buds 3–4-flowered); emerging leaves: marginal teeth eglandular | > 75 |
| 75 | Hypanthial exterior and sepal abaxial surfaces glabrous. | Prunus americana |
| 75 | Hypanthial exterior (at least distally) and sepal abaxial surfaces hairy | > 76 |
| 76 | Shrubs or trees, suckering; twigs usually hairy; pedicels hairy. | Prunus americana |
| 76 | Trees, rarely suckering; twigs usually glabrous; pedicels usually glabrous, sometimes sparsely hairy. | Prunus mexicana |
| 77 | Emerging leaves: marginal teeth glandular, glands reddish orange, conic; sepals not 2-fid at apices. | Prunus angustifolia |
| 77 | Emerging leaves: marginal teeth eglandular or glandular, glands blackish, spheric; sepals sometimes 2-fid at apices | > 78 |
| 78 | Twigs, pedicels, and hypanthial exteriors glabrous. | Prunus umbellata |
| 78 | Twigs, pedicels, and hypanthial exteriors hairy | > 79 |
| 79 | Hypanthia tubular (often tubular-urceolate when dried); trees or shrubs, 10–60 dm. | Prunus umbellata |
| 79 | Hypanthia campanulate; shrubs, 3–25 dm | > 80 |
| 80 | Leaves, emerging: usually eglandular, rarely glandular; flowering Apr–Jun; Atlantic seaboard. | Prunus maritima |
| 80 | Leaves, emerging: often with spheric glands on marginal teeth; flowering Mar–Apr; s Great Plains. | Prunus gracilis |
| 81 | Emerging leaves: marginal teeth eglandular; sepals irregularly or obscurely glandular-toothed | > 82 |
| 81 | Emerging leaves: marginal teeth glandular; sepals regularly and conspicuously glandular-toothed | > 84 |
| 82 | Hypanthial exterior and sepal abaxial surfaces glabrous. | Prunus americana |
| 82 | Hypanthial exterior (at least distally) and sepal abaxial surfaces hairy | > 83 |
| 83 | Shrubs or trees, suckering; twigs usually hairy; pedicels hairy. | Prunus americana |
| 83 | Trees, rarely suckering; twigs usually glabrous; pedicels usually glabrous, sometimes sparsely hairy. | Prunus mexicana |
| 84 | Inflorescences solitary flowers or 2-flowered fascicles | > 85 |
| 84 | Inflorescences 1–5-flowered (at least some buds on each plant 3–4-flowered) | > 88 |
| 85 | Petals 25+ (flowers lacking stamens and carpels). | Prunus glandulosa |
| 85 | Petals 5 (flowers with stamens and carpels) | > 86 |
| 86 | Pedicels 0.5–5(–8) mm; hypanthia 1.5–2.5 mm; petals 4–8 mm; plants thorny. | Prunus spinosa |
| 86 | Pedicels (2–)10–20 mm; hypanthia 2–5 mm; petals 7–14 mm; plants not or slightly thorny | > 87 |
| 87 | Twigs and pedicels glabrous; sepals 2–4 mm, margins eciliate. | Prunus cerasifera |
| 87 | Twigs and pedicels usually hairy; sepals 3.5–6 mm, margins ciliate. | Prunus domestica |
| 88 | Twigs with terminal end buds; plants not thorny | > 89 |
| 88 | Twigs with axillary end buds; plants usually thorny | > 91 |
| 89 | Shrubs, 1–15(–25) dm; hypanthia 1.7–3 mm. | Prunus pumila |
| 89 | Shrubs or trees, 30–100 dm; hypanthia 4–7 mm | > 90 |
| 90 | Twigs, pedicels, hypanthia glabrous; sepals reflexed. | Prunus cerasus |
| 90 | Twigs, pedicels, hypanthia hairy; sepals erect to spreading. | Prunus subhirtella |
| 91 | Sepals 2.2–4(–5) mm; hypanthia 2–3.5 mm (sepals longer than hypanthia); California, Oregon. | Prunus subcordata |
| 91 | Sepals 1.5–4(–5) mm; hypanthia 2–4(–5) mm (sepals equal to or shorter than hypanthia); e of Rocky Mountains | > 92 |
| 92 | Petals 8–13 mm; hypanthia 3–4(–5) mm, red-tinged. | Prunus nigra |
| 92 | Petals 4–9 mm; hypanthia 2–3 mm, green | > 93 |
| 93 | Twigs and pedicels hairy. | Prunus murrayana |
| 93 | Twigs and pedicels glabrous | > 94 |
| 94 | Leaf blades lanceolate, oblong-lanceolate, or elliptic to narrowly elliptic, (usually folded along midribs); plants usually suckering; shrubs or trees, 10–80 dm; pedicels 3–15 mm. | Prunus rivularis |
| 94 | Leaf blades narrowly elliptic, lanceolate, oblanceolate, or oblong-obovate, (not folded along midribs); plants rarely suckering; trees, 40–100 dm; pedicels 8–20 mm. | Prunus hortulana |
"thin" is not a number.