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Keyed in multiple places:

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Key to Thalictrum

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1 Sepals petaloid, conspicuous, white (or tinged with pink or green); leaflike involucral bracts present, opposite or whorled; inflorescence an umbel; [section Anemonella]
1 Sepals absent, or inconspicuous in comparison to the stamens or pistils; leaflike involucral bracts not present; inflorescence a panicle, corymb or raceme.
..2 Fruit (achene) scimitar-shaped, borne on a stipe 1.5-4 mm long; flowers perfect; [section Physocarpum].
....3 Achene concave or straight on the upper surface, 4-5.5 mm long, borne on a stipe 1.5-3 mm long; inflorescence branches stiff and diverge at acute angles; [fairly widespread in our area, on a wide variety of moist substrates, especially in the Mountains]
....3 Achene straight on the upper surface, 2.5-4 mm long, borne on a stipe 2.5-4 mm long; inflorescence branches flexuous and divergent; [of sandstone rockhouses of Cumberland Plateau of AL, TN, and KY]
..2 Fruit (achene) not scimitar-shaped, not borne on a stipe (except T. coriaceum); flowers unisexual (or sometimes a few or more bisexual).
......4 Leaflets of the stem leaves linear to narrowly lanceolate, oblanceolate or elliptic, (3-) 5-10 (-25)× as long as wide; [section Leucocoma]
......4 Leaflets of the stem leaves ovate, obovate, or suborbicular, 0.7-3 (-5)× as long as wide.
........5 Most of the leaflets with (3-) 4-6 (-9) lobes or teeth; [section Heterogamia].
..........6 Cauline leaf subtending the lowest flowering branch sessile; plant flowering May-Jul; achenes borne on a 0.7-2.5 mm long stipe
..........6 Cauline leaf subtending the lowest flowering branch with a petiole 3-7 cm long; plant flowering Mar-Apr; achenes nearly sessile, the stipe nonexistent or <0.3 mm long.
............ 7 Largest leaflets > 15 mm long; stems 30-80 cm tall, erect
............ 7 Largest leaflets < 15 mm wide; stems 10-40 (-45) cm tall, reclining or erect.
............ ..8 Achenes 0.7-1.2 mm thick, with 6-8 veins; achene beak 1.3-3.0 mm long; [GA west to MS; east of MS river]
............ ..8 Achenes 1.4-2.0 mm thick, with 6-8 veins (T. texanum) or 10-12 veins (T. arkansanum); achene beak 1.3-3.0 mm long; [AR, OK, TX; west of MS river].
............ ....9 Plants reclining; stigmas 1.3-3 mm long; achenes ellipsoid; roots brown when dry; [ne. TX, adjacently in OK and AR]
............ ....9 Plants erect; stigmas 0.5-1 mm long; achenes ovoid; roots black when dry; [se. TX]
........5 Most of the leaflets with 1-3 (-5) lobes or teeth; [section Leucocoma].
............ ......10 Leaflet undersurfaces, peduncles, and achenes with stipitate glands or papillae.
............ ........11 Anthers 1-3.6 (-4) mm long; stigmas 1.5-4.7 (-6) mm long
............ ........11 Anthers 0.5-2.8 mm long; stigmas 0.6-3.5 mm long.
............ ..........12 Anthers 0.5-1.2 mm long; stigmas 0.6-2.2 mm long
............ ..........12 Anthers 1.5-2.8 mm long; stigmas (1.5-) 2.0-3.5 mm long
............ ......10 Leaflet undersurfaces, peduncles, and achenes glabrous or pubescent, lacking both stipitate glands and papillae.
............ ............ 13 Leaflet undersurfaces, peduncles, and achenes finely pubescent
............ ............ 13 Leaflet undersurfaces, peduncles, and achenes glabrous to glabrate (rarely all three in T. pubescens, but keyed below as a fail-safe).
............ ............ ..14 Leaflets entire to 3-lobed, averaging about 10 mm wide, the broadest usually < 20 mm wide; filaments (2-) 3-4.5 (-6.5) mm long (averaging 3.6 mm)
............ ............ ..14 Leaflets 3-lobed (rarely entire), averaging 15-23 mm wide, the broadest usually (5-)15-60 (-70) mm wide; filaments (1.5-) 4-5 (-8) mm long (averaging 4.5 mm).
............ ............ ....15 Anthers 1-3.6 (-4) mm long; stigmas 1.5-4.7 (-6) mm long
............ ............ ....15 Anthers 0.5-2.8 mm long; stigmas 0.5-3.5 mm long.
............ ............ ......16 Leaflets and achenes lacking stipitate glands or papillae; filaments somewhat to prominently dilated distally (clavate); achenes often with a coiled beak (sometimes straight)
............ ............ ......16 Leaflets and achenes usually with stipitate glands or papillae, if glabrous then plants also with filiform filaments and achene beaks linear-filiform and lacking curvature.
............ ............ ........17 Anthers 0.5-1.2 mm long; stigmas 0.6-2.2 mm long
............ ............ ........17 Anthers 1.5-2.8 mm long; stigmas (1.5-) 2.0-3.5 mm long

Key C: Subkey in Ranunculaceae

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1 Leaflets linear, < 1.5 mm wide.
..2 Flowers bilaterally symmetrical; [subfamily Ranunculoideae, tribe Delphineae]
..2 Flowers radially symmetrical.
....3 Aquatic; [native]; [subfamily Ranunculoideae, tribe Ranunculeae]
....3 Terrestrial; [alien].
......4 Flower closely subtended by a finely dissected involucre; pistils compound; [subfamily Ranunculoideae, tribe Nigelleae]
......4 Flower lacking involucre; pistils simple.
........5 Petals 8-15 mm long, red, purple, or orange; [subfamily Ranunculoideae, tribe Adonideae]
........5 Petals 3-5 mm long, yellow; [subfamily Ranunculoideae, tribe Ranunculeae]
1 Leaflets broader, rounded, lobed, or toothed.
..........6 Leaves all cauline, opposite; stems somewhat woody at base; [subfamily Ranunculoideae, tribe Anemoneae]
..........6 Leaves basal and cauline, the cauline alternate (or with opposite or whorled involucral bracts).
............ 7 Petals present, conspicuous
............ ..8 Flowers dangling; petals red, orange with yellow, or blue, spurred; [subfamily Thalictroideae]
............ ..8 Flowers not dangling; petals yellow, not spurred; [subfamily Ranunculoideae, tribe Ranunculeae]
............ 7 Petals absent or inconspicuous (soon deciduous or altered into a nectary-bearing clavate structure); sepals sometimes petaloid and conspicuous.
............ ....9 Sepals petaloid, conspicuous, white (or cream, rose, pink, or tinged with green).
............ ......10 Involucre absent, all leaves on the stem alternate; petaloid sepals 5, white; [subfamily Thalictroideae]
............ ......10 Involucre of opposite or whorled, leaflike bracts present; petaloid sepals (4-) 5-20 (-30), white, cream, rose, or green.
............ ........11 Basal leaves with 3-5 leaflets, these toothed or incised; petaloid sepals white, cream, rose, or green; [subfamily Ranunculoideae, tribe Anemoneae]
............ ........11 Basal leaves with > 5 leaflets; these with 0-3 rounded lobes at the tip; petaloid sepals white to pale pink; [subfamily Thalictroideae]
............ ....9 Sepals absent, or inconspicuous in comparison to the stamens or pistils.
............ ..........12 Leaflets 3; flower solitary; [subfamily Coptidoideae]
............ ..........12 Leaflets many; flowers many, in a panicle or raceme.
............ ............ 13 Inflorescence a raceme; [subfamily Ranunculoideae, tribe Cimicifugeae]
............ ............ 13 Inflorescence a panicle; [subfamily Thalictroideae]

Key D: Subkey in Ranunculaceae

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1 Fruit a follicle or capsular (or fleshy and berrylike in some Actaea).
..2 Mature leaves > 4 dm wide; [subfamily Ranunculoideae, tribe Cimicifugeae]
..2 Mature leaves < 3 dm wide.
....3 Leaflets linear; [aliens].
......4 Flowers in a raceme, not subtended by an involucre; fruit follicular, each with a 1-2 mm long beak; [subfamily Ranunculoideae, tribe Delphineae]
......4 Flower solitary, subtended by a finely divided involucre; fruit a spherical capsule-like structure composed of 5 or 10 partially connate follicles, each follicle terminated by a linear beak 13-20 mm long; [subfamily Ranunculoideae, tribe Nigelleae]
....3 Leaflets broad, rounded; [mostly natives].
........5 Follicles borne on stipes, forming an umbel-like cluster; rhizomes yellow or orange; [subfamily Coptidoideae]
........5 Follicles sessile; rhizomes brown or tan; [subfamily Thalictroideae].
..........6 Follicles 15-31 mm long, with beaks 7-18 mm long
..........6 Follicles 3.5-6.5 mm long, with beaks 1.5-3 mm long
1 Fruit an achene.
............ 7 Leaves divided into numerous linear segments, all of which are < 1 mm wide.
............ ..8 Plant aquatic (if leaves divided into numerous linear segments); [subfamily Ranunculoideae, tribe Ranunculeae]
............ ..8 Plant terrestrial.
............ ....9 Achenes 3-5 mm long, glabrous, with a persistent beak 0.5-1 mm long; [subfamily Ranunculoideae, tribe Adonideae]
............ ....9 Achenes 1.6-2 mm long, tometose, with a persistent beak 3.5-4.5 mm long; [subfamily Ranunculoideae, tribe Ranunculeae]
............ 7 Leaf segments rounded or cleft, > 1 mm wide.
............ ......10 Leaves cauline, opposite; [subfamily Ranunculoideae, tribe Anemoneae]
............ ......10 Leaves basal and/or cauline, cauline leaves (if present) alternate (leaflike involucral bracts sometimes present and opposite or whorled).
............ ........11 Leaflike involucral bracts present, opposite or whorled.
............ ..........12 Achenes not ribbed or veined on lateral surfaces; leaf texture moderate to distinctly thick and leathery; [subfamily Ranunculoideae, tribe Anemoneae]
............ ..........12 Achenes conspicuously ribbed or veined on lateral surfaces; leaf texture thin, delicate; [subfamily Thalictroideae]
............ ........11 Leaflike involucral bracts not present.
............ ............ 13 Leaflets 3-many, if many the leaflets typically with teeth, or sharp lobes; [subfamily Ranunculoideae, tribe Ranunculeae]
............ ............ 13 Leaflets many, unlobed or typically with 3-9 rounded lobes; [subfamily Thalictroideae]
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