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Key to Physostegia

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1 Leaves petiolate or sessile, none of them clasping the stem.
  2 All or most of the largest leaves sharply serrate; apex of the leaves acute to attenuate.
    3 Axis of raceme with at least some of the hairs 0.13-0.25 mm long; nutlets 2-3 mm long; flowering Apr to early Jul (or later if burned)
    3 Axis of raceme with hairs < 0.1 mm long; nutlets usually 3-4 mm long; flowering Jul-Oct.
      4 Perennating buds usually borne directly on the primary rhizome or at the ends of short, vertical secondary rhizomes (horizontal secondary rhizomes usually lacking), the plant thus forming clumps; nonglandular trichomes of the raceme axis < 0.1 (-0.13) mm long; sterile floral bracts usually present below lowest flowers; flowers (16-) 18-37 mm long
      4 Perennating buds usually borne at the ends of elongate, horizontal, secondary rhizomes, the plant thus forming clonal patches; nonglandular trichomes of the raceme axis frequently 0.15-(-0.20) mm long; sterile floral bracts usually not present below lowest flowers; flowers (13-) 14-28 mm long
  2 Half or more of the larger leaves bluntly toothed to entire; apex of the leaves obtuse, or acute to attenuate.
        5 Calyx and rachis of the inflorescence bearing stalked glands (visible at 10× magnification or greater); nutlets 1.7-2.0 mm long, usually warty over the surface
        5 Calyx and rachis lacking stalked glands; nutlets 2.0-3.6 mm long, smooth.
          6 Uppermost pair of leaves below the terminal raceme often no larger than the floral bracts, the next pair of leaves down the stem 0.4-3.2 cm long, generally 0.1-0.3× as long as the internode above
          6 Uppermost pair of leaves below the terminal raceme usually considerably larger than the floral bracts, the next pair of leaves down the stem (1.5-) 2.0-12.8 cm long and 0.3-2× as long as the internode above.
             7 Leaves (some of them) present at or after anthesis usually petiolate, the petioles often > 2 cm long, the petiolate leaves typically the lowest and among the largest leaves present
             7 Leaves present at or after anthesis usually sessile (rarely a few petiolate, but these with petioles < 2 cm long and the petiolate leaves usually not among the largest leaves present)
1 Leaves, 1 or more of them, conspicuously or inconspicuously clasping the stem.
               8 Perennating buds borne directly on the primary rhizome or at the ends of short, vertical secondary rhizomes (horizontal secondary rhizomes lacking), the plant thus forming clumps
                 9 Most or all of the larger leaves sharply serrate; larger leaves usually < 2.5 cm wide and > 5× as long as wide
                 9 Most or all of the larger leaves bluntly serrate to entire; larger leaves usually > 3 cm wide or < 5× as long as wide.
                   10 Raceme axis densely tomentose, the hairs mostly 0.2-0.3 mm long; calyx lobes at anthesis generally 2-3 mm long, attenuate or cuspidate
                   10 Raceme axis puberulent to pubescent, the hairs almost all < 0.2 mm long; calyx lobes at anthesis generally 1-2 mm long, mostly acute
               8 Perennating buds borne at the ends of elongate, horizontal, secondary rhizomes, the plant thus forming clonal patches.
                     11 Calyx and inflorescence rachis bearing stalked glands as well as nonglandular hairs; leaves mainly 2-3× as long as wide
                     11 Calyx and rachis with nonglandular hairs only; leaves mostly > 3.5× as long as wide.
                       12 Flowers 22-35 mm long; larger stem leaves acute to attenuate at the tip; axis of raceme with at least some of the hairs 0.13-0.25 mm long; larger stem leaves mostly sharply serrate
                       12 Flowers smaller, or most of the leaves obtuse at the tip, or hairs of the raceme axis < 0.13 mm long; larger stem leaves bluntly toothed to entire.
                          13 Flowering calyx tube (1-) 2-4 mm long; flowers < 20 mm long
                          13 Flowering calyx tube 3-7 (-8) mm long; flowers usually > 20 mm long.
                            14 Uppermost pair of leaves below the terminal raceme usually considerably larger than the floral bracts, the next pair of leaves down the stem (1.5-) 2.0-12.8 cm long and 0.3-2× as long as the internode above; principal stem leaves usually widest at or below the middle of the blade
                            14 Uppermost pair of leaves below the terminal raceme often no larger than the floral bracts, the next pair of leaves down the stem 0.4-3.2 cm long, generally 0.1-0.3× as long as the internode above; principal stem leaves usually widest at or above the middle of the blade