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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].
                   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 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