Flora of the Southeastern United States
2022 Edition

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Key to Thalictrum

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 cm tall, reclining
............ ..8 Achenes 1.5-2.0 mm thick, with 10-12 veins; achene beak (1.3-) 2.3-3.0 mm long; [AR, se. OK, and ne. TX]
............ ..8 Achenes 0.7-1.2 mm thick, with 6-8 veins; achene beak 1.3-3.0 mm long; [GA west to MS]
........5 Most of the leaflets with 1-3 (-5) lobes or teeth; [section Leucocoma].
............ ....9 Leaflet undersurfaces, peduncles, and achenes with stipitate glands or papillae.
............ ......10 Anthers 1-3.6 (-4) mm long; stigmas 1.5-4.7 (-6) mm long
............ ......10 Anthers 0.5-2.8 mm long; stigmas 0.6-3.5 mm long.
............ ........11 Anthers 0.5-1.2 mm long; stigmas 0.6-2.2 mm long
............ ........11 Anthers 1.5-2.8 mm long; stigmas (1.5-) 2.0-3.5 mm long
............ ....9 Leaflet undersurfaces, peduncles, and achenes glabrous or pubescent, lacking both stipitate glands and papillae.
............ ..........12 Leaflet undersurfaces, peduncles, and achenes finely pubescent
............ ..........12 Leaflet undersurfaces, peduncles, and achenes glabrous.
............ ............ 13 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)
............ ............ 13 Leaflets 3-lobed (rarely entire), averaging 15-23 mm wide, the broadest usually 15-60 mm wide; filaments (2-) 4-5 (-8) mm long (averaging 4.5 mm).
............ ............ ..14 Anthers 1-3.6 (-4) mm long; stigmas 1.5-4.7 (-6) mm long
............ ............ ..14 Anthers 0.5-2.8 mm long; stigmas 0.6-3.5 mm long.
............ ............ ....15 Anthers 0.5-1.2 mm long; stigmas 0.6-2.2 mm long
............ ............ ....15 Anthers 1.5-2.8 mm long; stigmas (1.5-) 2.0-3.5 mm long