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Key to Thalictrum

Ranunculaceae

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].
                          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).
                                16 Leaflets and achenes lacking stipitate glands or papillae; filaments somewhat to prominently dilated distally (clavate); achenes often with a coiled beak (sometimes straight)