Pycnanthemum

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  P. incanum

  1a. Inflorescence congested but many of the branches within the clusters visible, especially in fruit [Fig. 702], the individual clusters 15–35 (–45) mm wide; calyx zygomorphic, the upper lip definitely shorter than the lower lip, the lobes tipped with a tuft of long, septate hairs
• See list of 5 species in 1b
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  1b. Inflorescence very dense, only the lowest branches, if any, visible [Fig. 703], the individual clusters 3–15 (–20) mm wide; calyx ± actinomorphic, the lobes lacking a tuft of long, septate hairs (though other hairs may be present)
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    P. muticum

    2a. Principal leaf blades lanceolate to ovate, 12–30 (–40) mm wide, mostly less than 
2.5 times as long as wide, rounded at the base, with a few low teeth on each margin
  • See list of 4 species in 2b
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    2b. Principal leaf blades linear to lanceolate, 2–12 (–15) mm wide, mostly more than 2.5 times as long as wide, cuneate at the base, with or without teeth
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      P. tenuifolium

      3a. Leaf blades 2–4 (–5.5) mm wide, sessile, glabrous [Fig. 703]; stem glabrous or rarely with a few upcurved hairs on the angles; calyx lobes 1–1.5 mm long
    • See list of 3 species in 3b
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      3b. Leaf blades 3–12 (–15) mm wide, short-petioled to subsessile, pubescent on at least the abaxial surface; stem pubescent on the angles and sometimes the faces as well; calyx lobes 0.5–1 mm long (up to 1.5 mm long in P. torrei)
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        P. verticillatum

        4a. Bracts, and often also the leaf blades, pubescent on the adaxial surface with minute, soft hairs (view at 20 ×); stems pubescent on the faces as well as the angles
      • See list of 2 species in 4b
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        4b. Bracts and leaf blades glabrous on the adaxial surface (sometimes with minute, stiff scabrules on the adaxial bract surface); stems pubescent primarily on the angles or also pubescent on the faces in P. torrei
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          P. virginianum

          5a. Calyx lobes triangular, 0.5–1 mm long; pubescence of stem confined chiefly to the angles; leaf blades entire
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          P. torrei

          5b. Calyx lobes narrow-lanceolate, 1–1.5 mm long; pubescence of stem uniformly distributed; leaf blades usually with a few low teeth

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 Show photos of:   Each photo represents one species in this genus.