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Key to Potentilla

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1 Leaves pinnately compound, with (5-) 7-21 (-31) leaflets.
..2 Leaves with (5-) 7-21 (-31) leaflets; flowers solitary, on naked, axillary pedicels; lower leaf surface silvery-white, densely appressed-hairy
..2 Leaves with 5-9 leaflets; flowers (10-) 20-100 (or more) in a cyme or raceme; lower leaf surface green, glabrate or sparsely hairy; [section Rivales]
1 Leaves palmately compound, with 3-9 leaflets.
....3 Flowers solitary, on naked, axillary pedicels; leaves either palmately 3-5-foliolate or pinnately (5-) 7-21 (-31)-foliolate.
......4 Leaves 3-foliolate; fruit strawberry-like, fleshy and red, consisting of an expanded fleshy receptacle bearing superficial achenes; [formerly genus Duchesnea]
......4 Leaves primarily 5-foliolate on a plant (some poorly developed leaves may be 3-4-foliolate); fruit a head of achenes, dry; [section Potentilla].
........5 Sepals 4; petals 4; stems branching when well-developed; leaves with 3-5 leaflets; [rare waif]
........5 Sepals 5; petals 5; stems not branching; leaves with 5 leaflets (fewer only on smaller or poorly developed leaves); [collectively common and widespread].
..........6 Plants lacking rhizomes; petals (6-) 8-12 mm long; anthers 1.3-2.0 mm long
..........6 Plants with horizontal rhizomes; petals 4-10 mm long; anthers 0.6-1.0 mm long.
............ 7 Terminal leaflet (of well-developed leaves) toothed for < ½ its length, with 2-7 teeth per leaflet side; terminal leaflet usually < 2× as long as wide; lowest flower produced from the axil of the 1st stem leaf above the plant base, typically with only 1 leaf and pedicel at each subsequent node; plants often flowering on short stolons obscured by basal leaves; stem usually prostrate from the beginning, 0.3-0.8 mm in diameter
............ 7 Terminal leaflet (of well-developed leaves) toothed for > ½ its length, with 4-8 (-13) teeth per leaflet side; terminal leaflet usually > 2× as long as wide; lowest flower produced from the axil of the 2nd stem leaf above the plant base, typically with 2 leaves and 1 pedicel at each subsequent node; plants only flowering on elongating stolons; stem usually erect initially, 0.9-1.4 mm in diameter
....3 Flowers in terminal cymes; leaves palmately 3-9-foliolate.
............ ..8 Leaves 3-foliolate (sometimes with some leaves 5-foliolate); [section Rivales].
............ ....9 Hairs of the stem stiff, tubercle-based, to 3 mm long; petals (2-) 3-5 mm long; stamens (15-) 20; achenes usually ridged, tan or brown, 0.8-1.3 mm long
............ ....9 Hairs of the stem weak, not tubercle-based, to 1.5 mm long; petals 1.5-2 mm long; stamens (5-) 10 (-15); achenes smooth, white or yellowish, 0.7-0.9 mm long
............ ..8 Leaves 5-9-foliolate.
............ ......10 Leaves (5-) 7-9-foliolate; petals 8-15 mm long, pale (sulfur) yellow; [section Rectae]
............ ......10 Leaves 5 (-7)-foliolate; petals 3-7 (-8) mm long, medium yellow; [section Terminales].
............ ........11 Leaves pubescent beneath, the green surface not concealed; petals 4-5 mm long
............ ........11 Leaves densely tomentose beneath, the surface concealed; petals either 2.5-4 mm long or 5-7 (-8) mm long.
............ ..........12 Pubescence of the stem and veins of the leaf undersurface tomentose only; lower leaf surface silvery-white tomentose; leaves revolute; petals 2.5-4 mm long
............ ..........12 Pubescence of the stem and veins of the leaf undersurface tomentose and also with long, spreading hairs; lower leaf surface somewhat to strongly grayish-tomentose; leaves not revolute; petals 5-7 (-8) mm long

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.
............ ............ ......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
............ ............ ............ 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 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
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