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Key to Helianthus, Key C: perennial sunflowers with leafy stems and red disk flowers

Asteraceae

Helianthus

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1 Stems glabrous or glabrate and often glaucous; leaf margins not revolute.
  2 Plant 4-7 dm tall; blades of ray flowers 8-9 mm long; leaf blades 3-7.5 cm long
  2 Plant 15-25 or more dm tall; blades of ray flowers 28-35 mm long; leaf blades 8-21 cm long
    3 Leaf blades long and narrow, linear or lanceolate and usually > 10× as long as wide.
      4 Plants < 1.5 m tall; leaves < 1 cm wide; rhizomes lacking or poorly developed
      4 Plants > 1.5 m tall; leaves > 1 cm wide; rhizomes well developed
    3 Leaf blades shorter and broader, lanceolate, lance-ovate, deltoid, deltoid-ovate and usually < 5× as long as wide.
          6 Abaxial surfaces of leaves and ligules lacking subsessile glandular trichomes; leaves usually broadly ovate to orbicular and with a petiole > 1 cm long
          6 Abaxial surfaces of leaves and ligules with subsessile glandular trichomes; leaves usually lanceolate to lance-ovate or rhombic-ovate and with a petiole usually < 1 cm long.
               8 Plants 8-20 dm tall; upper leaves usually alternate; leaf blades oblong-lanceolate to lance-ovate, 8-27 cm long, acuminate at tip
               8 Plants 5-12 dm tall; leaves opposite; leaf blades rhombic-ovate to lance-linear, 5-12 cm long, acute or obtuse at tip