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Key to Rosaceae

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1 Herbs or subshrubs (if woody at base, then < 3 dm tall).
..2 Leaves simple
..2 Leaves compound (at least the lower and better developed)
1 Trees, shrubs, or woody vines (with arching “canes” or climbing, arching, or scrambling stems).
....3 Leaves simple
....3 Leaves compound

Key to Rosaceae, Key A: Herbs and subshrubs with simple leaves

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1 Leaves crenate, unlobed; inflorescence of a solitary flower; [tribe Rubeae]
1 Leaves 3-9 lobed; inflorescences cymose.
..2 Leaves shallowly 7-9-lobed; petals 0; stamens 4.
..2 Leaves 3-lobed; petals 0 or 5; stamens 1 or many.
....3 Leaf blades 0.3-1.0 cm long and wide, deeply 3-lobed, each lobe further lobed or deeply toothed; petals 0; stamen 1; [tribe Potentilleae]
....3 Leaf blades 3-8 cm long and wide, 3-lobed, each lobe toothed; petals 5; stamens many; [tribe Colurieae]

Key to Rosaceae, Key B: Herbs and subshrubs with compound leaves

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1 Leaves 2- to 3-ternately compound; [tribe Spiraeeae]
1 Leaves 1-compound, either simply pinnately compound or simply palmately compound,
..2 Principal (basalmost) leaves pinnately compound, with (3-) 5-many leaflets (upper stem leaves sometimes 3-foliolate).
....3 Principal leaves with leaflets of markedly disparate shape and size (large leaflets alternating with much smaller leaflets, or a large terminal leaflet and much smaller lateral leaflets).
......4 Lateral leaflets alternating between small and large, the terminal leaflet similar in size and shape to the larger lateral leaflets; terminal leaflet < 3 cm wide; hypanthium either conical or turbinate, armed with hooked bristles, the pistils 2, or hemispheric, the pistils >5.
........5 Leaves glabrous or sparsely pubescent beneath; flowers many in racemes; hypanthium conical or turbinate, armed with hooked bristles, the pistils 2; [tribe Sanguisorbeae]
........5 Leaves silvery sericeous beneath; flowers solitary and axillary; hypanthium hemispheric, the pistils >5; [tribe Potentilleae]
......4 Leaflets variable in size and shape, usually the terminal leaflet much larger than any of the lateral leaflets; terminal leaflet 3-20 cm wide; hypanthium either sauce-r-shaped or hemispheric to conical; pistils 5 or more.
..........6 Pistils 5-15, in a circle on a saucer-shaped hypanthium, ripening into upright fruits that resemble follicles but are indehiscent; corolla white or pink; plant 10-20 dm tall; [tribe Ulmarieae]
..........6 Pistils many, densely covering the hemispheric to conical hypanthium, ripening into achenes terminated by the persistent style; corolla white, cream, pale yellow, bright yellow, lavender, maroon, or purple; plant 2-10 dm tall; [tribe Colurieae]
....3 Principal leaves with leaflets of generally similar shape and size (the lowest leaflets may be smaller but of similar shape and toothing to the other leaflets).
............ 7 Stems and leaf rachises and petioles armed with retrorse prickles.
............ 7 Stems and leaves unarmed.
............ ..8 Foliage and stems viscid-pubescent with brownish hairs; inflorescence a cyme; petals 5, cream-colored; [tribe Potentilleae]
............ ..8 Foliage not viscid-pubescent (if hairy, the hairs not brown or viscid); inflorescence of very many (>100) small flowers in a spike, the rachis hidden by the tightly packed flowers; petals 0; [tribe Sanguisorbeae].
............ ....9 Leaflets pinnatifid (each leaflet incised nearly to the midvein); stamens 2 or 4 per flower
............ ....9 Leaflets toothed (the incisions not nearly to the midvein); stamens either 4 or 15-20 per flower (in well-developed, staminate flowers).
............ ......10 Leaflets 0.8-2 cm long; spike 1-2 cm long, 1-2× as long as broad, globose; stamens 15-20 per flower (in well-developed staminate flowers), the filaments 3-4 mm long; sepals green to pinkish-purple; [cultivated, occasionally escaped]
............ ......10 Leaflets 3-10 cm long; spike 6-30 cm long, elongate; stamens 4 per flower, the filaments 8-10 mm long; sepals white (sometimes fading greenish); [native]
..2 Principal (basal-most) leaves palmately compound, with 3-7 (-9) leaflets.
............ ........11 Principal leaves subsessile, 3-foliolate; fruit of follicles; leaves cauline; [tribe Gillenieae]
............ ........11 Principal leaves distinctly petiolate, the petiole often longer than the leaflets, 3-7 (-9)-foliolate; fruit of achenes; leaves basal and cauline.
............ ..........12 Principal leaves 5-7 (-9)-foliolate; [tribe Potentilleae]
............ ............ 13 Petals maroon-colored, shorter than sepals; plants sprawling with horizontal stems bearing rooting nodes; [wetlands from n. PA, n. NJ, sc. IN and sc. OH northward]
............ ............ 13 Petals yellow or white, not shorter than sepals; plants trailing or upright, if bearing horiztonal stems with rooting nodes then petals not maroon-colored and plants not in wetlands; [dry habitats, collectively widespread]
............ ..........12 Principal leaves 3-foliolate.
............ ............ ..14 Plants in flower.
............ ............ ....15 Petals yellow.
............ ............ ......16 Pistils 2-6; [tribe Colurieae]
............ ............ ......16 Pistils (10-) numerous; [tribe Potentilleae]
............ ............ ....15 Petals white (or slightly pinkish).
............ ............ ........17 Calyx lobes not subtended by bractlets; [tribe Rubeae]
............ ............ ........17 Calyx lobes subtended by 5 sepaloid bractlets; [tribe Potentilleae].
............ ............ ..........18 Leaves evenly serrate with many serrations; [widespread]
............ ............ ..........18 Leaves with 3 (-5) teeth at the apex, otherwise entire
............ ............ ..14 Plants in fruit (or sterile).
............ ............ ............ 19 Leaflets entire, except for 3 (-5) teeth at the apex; [tribe Potentilleae]
............ ............ ............ 19 Leaflets evenly serrate or crenate, each well-developed leaflet with > 7 teeth.
............ ............ ............ ..20 Calyx lobes not subtended by bractlets.
............ ............ ............ ....21 Fruit an aggregate of dry, non-adherent achenes; leaflets obtuse at apex; [tribe Colurieae]
............ ............ ............ ....21 Fruit an aggregate of fleshy, adherent drupelets; leaflets acuminate at apex; [tribe Rubeae]
............ ............ ............ ..20 Calyx lobes subtended by 5 sepaloid bractlets; [tribe Potentilleae].
............ ............ ............ ......22 Fruit an aggregate of dry achenes
............ ............ ............ ......22 Fruit an accessory fruit of achenes borne on the surface of a fleshy, red receptacle.
............ ............ ............ ........23 Fresh fruit reddish inside; leaflets serrate, 2.5-12 cm long; sepaloid bracts narrowing to apex, untoothed
............ ............ ............ ........23 Fresh fruit whitish inside; leaflets crenate, 2-4 cm long; sepaloid bracts widest at apex, 3-5-toothed

Key to Rosaceae, Key C: Shrubs and trees with simple leaves

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1 Ovary inferior; fruit indehiscent (pome).
..2 Upper surface of leaves bearing dark glandular trichomes along the midrib (most easily seen with a 10× hand lens); shrubs
..2 Upper surface of leaves lacking dark glandular trichomes along the midrib; shrubs and trees.
....3 Ovary and fruit 10-locular; inflorescence a raceme (rarely a fascicle); pome < 1 cm in diameter
....3 Ovary and fruit 5-locular; inflorescence a cyme, umbel, or fascicle (lacking an elongated central axis); pome 0.7-10 cm in diameter.
......4 Styles distinct; exocarps (carpels within pericarp) bony and seedlike; trees and shrubs, with thorns
......4 Styles usually connate at base; exocarps leather or papery and easily opened to expose seeds; small trees, unarmed, or armed with sharp spur branches.
........5 Pome globose to ovoid, lacking stone cells; anthers yellow to white; styles connate at the base; leaves blunt to acuminate; [apples and crabapples]
........5 Pome globose or pyriform, with stone cells; anthers reddish; styles distinct; leaves acute to acuminate; [pears]
1 Ovary superior; fruit dehiscent (aggregate of follicles, or capsule) or indehiscent (drupe, aggregate of drupelets, aggregate of achenes).
..........6 Leaves opposite; fruit an aggregate of usually 3-5 purple to black drupelets; [tribe Kerrieae]
..........6 Leaves alternate; fruit various (see below; if an aggregate of drupelets, then with >5 drupelets).
............ 7 Leaves large, > 10 cm wide, palmately veined, palmately lobed; fruit an aggregate of drupelets; [tribe Rubeae]
............ 7 Leaves smaller, < 8 cm wide, pinnately veined, either not lobed or basally pinnately lobed; fruit a drupe, a capsule, an aggregate of follicles, or an aggregate of achenes.
............ ..8 Leaves singly serrate or entire (rarely, as in Prunus americana, irregularly and slightly doubly serrate), not lobed basally.
............ ....9 Gynoecium of separate carpels; fruit an aggregate of follicles; [tribe Spiraeeae]
............ ....9 Gynoecium of fused carpels; fruit either a fleshy drupe or a capsule.
............ ......10 Ovary 5-angled in ×-section; fruit a 5-angled capsule; leaves obovate, obviously broadest towards the tip; [tribe Osmaronieae]
............ ......10 Ovary circular in ×-section; fruit a fleshy spherical drupe; leaves generally broadest near or below the middle; [tribe Amygdaleae]
............ ..8 Leaves doubly serrate, also often lobed towards the base.
............ ........11 Corolla yellow; stems arching, green; fruit an aggregate of drupe-like achenes (dry and indehiscent); [tribe Kerrieae]
............ ........11 Corolla white to pink or rose; stems not both arching and green; fruit various (see below).
............ ..........12 Inflorescence a dense, umbel-like corymb; leaf apices rounded to acute; fruit an aggregate of 5 follicles; [tribe Neillieae]
............ ..........12 Inflorescence a raceme or a leafy panicle; leaf apices acuminate.
............ ............ 13 Fruit a single follicle; [alien, planted, and rarely naturalized, as in e. VA]; [tribe Neillieae]
............ ............ 13 Fruit an aggregate of 2-4 drupe-like achenes; [rare native of calcareous habitats in sc. TN, nw. GA, n. AL, and disjunct westward in AR and MO]; [tribe Kerrieae]

Key to Rosaceae, Key D: Shrubs and trees with compound leaves

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1 Leaflets < 5 mm wide, entire; densely-branched shrub to 1 m tall; flowers yellow; [tribe Potentilleae]
1 Leaflets > 10 mm wide, serrate or crenate; shrubs, trees, or woody vines (see below); flowers white, pink, or purplish (rarely yellow in Rosa).
..2 Leaves 1-pinnately compound, generally with > 11 leaflets; inflorescence a terminal panicle or corymb with numerous (> 100) flowers, the petals white and < 4 mm long; fruit a pome or follicle; upright tree or shrub with unarmed stems.
....3 Inflorescence a panicle; fruit a follicle; shrub, to 2 m tall; [tribe Sorbarieae]
....3 Inflorescence a corymb; fruit a pome; tree, generally > 2 m tall; [tribe Pyreae]
..2 Leaves palmately or 1-pinnately compound, generally with < 11 leaflets; inflorescences axillary or terminal panicles or corymbs with few (<15) flowers, the petals white, pink, or purplish (rarely yellow) and > 6 mm long; fruit a hip or aggregate of drupelets; arching or upright shrubs or climbing or sprawling woody vines, the stems usually armed with prickles.
......4 Fruit a hip, developing from a globose to urceolate hypanthium, enclosing the ovaries and achenes, except for the apical orifice; leaflets usually acute to obtuse at the apex; leaflet margins crenulate or serrulate; [tribe Roseae]
......4 Fruit an aggregate of drupelets, developing from a flattish or hemispheric hypanthium, with the ovaries and drupelets exposed; leaflets usually acuminate at the apex; leaflet margins serrate or doubly serrate; [tribe Rubeae]