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

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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
1 Stems pubescent, not glaucous; leaf margins revolute or not.
    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.
        5 Phyllaries 1.5-3 mm broad, lanceolate
        5 Phyllaries 3-5 mm broad, oblong, ovate, or obovate.
          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.
             7 Phyllaries oblong-lanceolate, apex acuminate, abaxially usually pubescent
             7 Phyllaries elliptical to oblong-ovate, apex acute, abaxially glabrate.
               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

Key to Helianthus, Key D: perennial sunflowers with leafy stems and yellow disk flowers

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1 Stems below the capitulescence glabrous or nearly so, sometimes glaucous.
  2 Leaves whorled at principal nodes, either alternate or opposite at other nodes
  2 Leaves either alternate or opposite (or both), never whorled.
    3 Leaves grayish-green or bluish green in color, sessile, and glabrous and glaucous on the undersurface.
      4 Rays 10-14; leaves strumose adaxially, rough to the touch; phyllaries 3.5-4.5 mm wide
      4 Rays 5-10; leaves glabrous or glabrate adaxially, smooth or only slightly rough to the touch; phyllaries 2-3 mm wide
    3 Leaves light to dark green, sometimes whitish abaxially, but not grayish or bluish green in color; leaves sessile or petiolate, glabrous or pubescent.
        5 Leaves linear-lanceolate, with only a single main vein
        5 Leaves linear-lanceolate to lanceolate, lance-ovate, or ovate, triplinerved at base.
          6 Rays few, usually 5 or 8; heads small, the involucres 9 mm broad or less.
             7 Leaves abaxially whitish in color and glabrous and glaucous, lacking subsessile glandular trichomes (‘resin dots’)
             7 Leaves abaxially greenish in color, usually tomentulose (sometimes glabrate), with abundant subsessile glandular trichomes
          6 Rays usually 10 or more in larger heads; heads larger, the involucres usually > 9 mm broad.
               8 Leaves sessile, rounded to cordate at base, and trinerved, with the 2 lateral veins diverging from the midrib at the very base of the leaf
               8 Leaves sessile to petiolate, but narrowing gradually to base and triplinerved, the 2 lateral veins diverging from the midrib above the base of the blade.
                 9 Anther appendages yellow.
                   10 Leave blade lanceolate to lance-ovate, sessile to petiolate but the petiole usually < ¼ as long as the blade; phyllaries not conspicuously graduated and imbricate, usually loose and spreading
                   10 Leaf blade ovate to elliptic, with a distinct petiole usually > 2 cm long and ½ as long as blade or longer; phyllaries conspicuously graduated and imbricate, usually appressed, not exceeding disk
                 9 Anther appendages dark or reddish-brown.
                     11 Plants producing abundant tubers; leaves subsessile, the petioles < 1 cm long; [endemic to the Piedmont of NC and SC]
                     11 Plants rhizomatous, but not producing tubers; leaves petiolate, the petioles 1-5 cm long; [collectively widespread in our area].
                       12 Longer phyllaries usually exceeding disk by ½ their length or more, apex acuminate; larger leaves moderately to conspicuously serrate, with a petiole 2-5 cm long, and abaxially with usually relatively few subsessile glandular trichomes
                       12 Phyllaries equal to or slightly exceeding disk, apex acute; leaves moderately serrate to entire, with a petiole 1-3 cm long, and abaxially with usually abundant subsessile glandular trichomes (‘resin dots’)
1 Stems pubescent throughout, not glaucous.
                          13 Leaves sessile and cordate, mostly or all opposite
                          13 Leaves petiolate or sessile, but not cordate, and alternate or opposite.
                            14 Phyllaries attenuate, conspicuously exceeding the disk in length and reflexed, apically with numerous subsessile glandular trichomes (‘resin dots’); leaf bases often convex, the basically ovate or lance-ovate blade joined to a broadly winged and gradually narrowed petiole
                            14 Phyllaries acute to attenuate, but not reflexed, subsessile glandular trichomes present or absent; leaf bases usually attenuate to truncate or rounded, the blade lance-linear or lanceolate, or if ovate or lance-ovate either sessile or with a petiole that is at most narrowly winged.
image of plant
Show caption*© Gary P. Fleming
                              15 Leaves conduplicate (strongly folded along the midvein, thus V-shaped in ×-section); leaf margins entire; leaf venation of a single prominent main vein (laterals not readily visible); inflorescence when well developed spiciform or racemose
                              15 Leaves flat or essentially so; leaf margins entire or serrate; leaf venation triplinerved (with a prominent lateral pair of veins near the base); inflorescence not spiciform or racemose.
                                16 Phyllaries conspicuously graduated and imbricate, usually appressed.
image of plant
Show caption*© Michael J. Oldham, some rights reserved (CC BY-NC), uploaded by Michael J. Oldham
                                  17 Leaf blades lanceolate to ovate, petiole 1-5 cm long and usually < ½ as long as blade; anther appendages with dark pigment; cypselas 4-5 mm, usually sterile
                                  17 Leaf blades ovate to elliptic, petiole distinct, > 2 cm and usually > ½ as long as the blade; anther appendages yellow; cypselas 3-4 mm long, fertile
                                    18 Leaves rough to touch, scabrous or hirsute; leaves entire or nearly so; [widely distributed]
                                    18 Leaves smooth to touch, strigose or glabrous; leaves usually serrate; [w. LA, AR, TX]
                                16 Phyllaries not conspicuously graduated and imbricate, usually loose or spreading.
                                       19 Leaves with a prominent petiole > 2 cm long, blades lance-ovate to ovate and > 5 cm broad; cypselas 5-7 mm long; tubers produced late in growing season
                                       19 Leaves sessile or with a short petiole usually < 2 cm long; blades linear to lanceolate, < 4.5 cm broad; cypselas 3-5 mm long; tubers present or absent.
                                         20 Leaves truncate to broadly rounded at base, shortly but distinctly petiolate
                                         20 Leaves cuneate, gradually narrowing to base, sessile to petiolate.
                                           21 Ligules lacking subsessile glandular trichomes; leaves not strongly revolute
                                           21 Ligules abaxially with subsessile glandular trichomes (‘resin dots’); leaves usually revolute.
                                             22 Heads relatively small, the disc portion of the heads usually < 15 mm across; abaxial leaf surfaces softly pubescent (on living plants, except the leaf margins and midveins which are scabrous); tubers present; [of the NC and SC piedmont]
                                             22 Heads various in size (8-20 mm+); abaxial leaf surfaces various, but not softly pubescent; tubers absent; [collectively widespread].
                                               23 Leaf margins conspicuously undulate, the blades narrowly lanceolate to ovate (occasionally linear, if so, usually < 10 cm long), mostly 3-veined (at mid-stem); inflorescences usually with 1-6 heads; plants rhizomatous; pappus scales aristate; [wet habitats, s. SC southward]
                                               23 Leaf margins not conspicuously undulate, the blades linear to lanceolate, mostly with a single prominent mid vein (at mid stem, sometimes the lowest leaves 3-veined); inflorescences with 1-16+ heads; plants rhizomatous or not; pappus scales aristate or not; [habitats various, collectively widespread]
                                                 24 Plants robust, > 1.5 m tall; leaves > 1 cm wide; plants conspicuously rhizomatous
                                                 24 Plants short, < 1.5 m tall; leaves < 1 cm wide; plants rhizomatous or not.
                                                    25 Plants usually > 1 m tall at maturity, not rhizomatous (from crowns or caudices); mid-stem leaves 8-20 cm long, alternate or opposite; inflorescences usually of 3-16+ heads; disc florets yellow, red, or purple; pappus scales narrowly lanceolate to aristate (0.1-0.3 mm wide, ≥7x as long as wide), lacking additional irregularly-shaped scales; [widespread]
                                                    25 Plants usually < 1 m tall at maturity, strongly rhizomatous; mid-stem leaves < 6 (-10) cm long, mostly opposite; inflorescences usually of 1-3 (-10) heads; disc florets yellow; pappus scales deltoid to lanceolate (usually ≥ 0.5mm wide, 1-4× as long as wide), often accompaned by additional irregularly-shaped scales; [Cape Fear Arch region of NC and SC]