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Keyed in multiple places:

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Key to Helenium

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1 Stem leaves very numerous, 0.5-2 (-4) mm wide, not decurrent on the stem or branches; taprooted annuals.
  2 Disc corollas yellow, the lobes yellow or yellow-brown; lower and basal leaves usually withered at anthesis; lower leaves usually entire (rarely toothed); basal leaves entire to toothed (rarely pinnatifid)
  2 Disc corollas yellow, the lobes (and sometimes also the upper portion of the corolla tube) purple; lower and basal leaves often persistent; lower leaves linear to ovate, entire, toothed, lobed or pinnatifid; basal leaves pinnatifid
1 Stem leaves few to numerous, at least the larger > 4 mm wide, decurrent on the stems and branches; fibrous-rooted perennials or taprooted annuals/biennials.
    3 Ray flowers absent; disc flowers with lobes (at least) brown, red, or purple
    3 Ray flowers present; disc flowers either yellow or with lobes (at least) brown, red, or purple.
      4 Ray flowers bearing a pistil and style, fertile.
        5 Plants fibrous-rooted perennials; [section Helenium].
          6 Leaves not basally disposed, the basal leaves usually absent at flowering (if present, mostly < 2 cm long), the stem leaves not progressively reduced upward; pappus scales brownish, 0.3-1.2 mm long (usually < 1 mm long); upper cauline leaves serrate (rarely entire), mostly oblanceolate, usually broadest near the midpoint or beyond it, with conspicuous lateral veins apparent on the lower surface
          6 Leaves basally disposed, the basal rosette usually present at flowering, the basal leaves > 4 cm long, larger than the progressively smaller stem leaves; pappus scales white-hyaline, 0.9-1.9 mm long (usually > 1 mm long); upper cauline leaves entire, lanceolate, usually broadest at or near the base and rather evenly tapered to the apex, lacking conspicuous lateral veins
        5 Plants tap-rooted annuals or biennials; [section Tetrodus].
             7 Involucres 6-11 (-14) mm high, 6-11 (-13) wide (excluding the ray flowers); disk corollas 4- or 5- lobed.
               8 Disc corollas 5-lobed; ray flowers 8-9, yellow or partially/wholly red; [TX]
               8 Disc corollas 4-lobed; ray flowers 10-15, yellow; [widely distributed]
             7 Involucres 4-8 mm high, 4-8 mm wide (excluding the ray flowers); disc corollas 5-lobed.
                 9 Upper leaves entire; pappus scales 0.05-0.2 mm long
                 9 Upper leaves serrate; pappus scales (0.2-) 0.3-0.4 (-0.5) mm long
      4 Ray flowers lacking a pistil and style, sterile; [section Leptopoda].
                   10 Disc flowers with lobes (at least) brown, red, or purple.
                     11 Disc flowers predominately 4-lobed and with 4 stamens; heads 5-50 (-80) per plant; pappus scales aristate
                     11 Disc flowers 5-lobed and with 5 stamens; heads 1-20 per plant; pappus scales acute.
                       12 Heads 1-5 (-10) per plant; pappus scales 1.0-1.7 mm long; basal leaves and lower stem glabrous to sparsely hairy; [VA west and south to ne. TN, s. MS, and e. LA]
                       12 Heads 3-20 per plant; pappus scales 0.3-0.5 mm long; basal leaves and lower stem moderately to densely hairy; [AR and n. LA]
                   10 Disc flowers with lobes yellow.
                          13 Pappus scales deeply lacerate
                          13 Pappus scales entire or slightly lacerate.
                            14 Midstem leaves barely decurrent on the stem, the decurrency < 0.5 cm; basal leaves often pinnatifid (less commonly merely dentate, repand, or entire), the lower portion of the leaf not contracted so as to be petiolate in form; achene pubescent on the ribs; peduncle pubescent; basal leaves (3.0-) 4.5-8.0 (-19.0) cm long, 0.3-1.1 cm wide, averaging ca. 7-10× as long as wide
                            14 Midstem leaves decurrent on the stem, the decurrency > 2 cm , and usually extending to the next leaf down; basal leaves usually repand or entire (rarely somewhat lobed or pinnatifid), the lower portion narrowed into a petiolate form which enlarges at its base to more-or-less clasp the stem; achene glabrous, or pubescent on the ribs; peduncle pubescent or glabrous; basal leaves averaging narrower or broader in shape (see below).
                              15 Peduncle pubescent to tomentose or lanose between the uppermost leaf and the head; achene pubescent on the ribs; heads 1-4 per plant; basal leaves (2.5-) 4.0-10.5 (-18.0) cm long, (0.8-) 1.2-2.0 (-2.5) cm wide, averaging ca. 4-6× as long as wide
                              15 Peduncle glabrous or glabrate between the uppermost leaf and the head; achene glabrous; heads 1 per plant; basal leaves (3.0-) 6.5-17.0 (-25.0) cm long, (0.4-) 0.6-1.0 (-1.5) cm wide, averaging ca. 10-15× as long as wide

Key to Asteraceae, Key I: Herbaceous composites with the leaves alternate, the heads lacking rays, and with a pappus wholly or partly of scales or awns

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1 Disc flowers yellow, orange, red, or brownish.
  2 Leaves 1-2× pinnately lobed into linear or filiform segments.
    3 Pappus of 16-20 scales
    3 Pappus of 6-10 scales; [historical waif]
  2 Leaves unlobed, or if pinnately lobed, the segments broad (> 3 mm wide).
      4 Receptacle paleate
      4 Receptacle epaleate.
        5 Pappus scales rudimentary, crown-like
        5 Pappus scales conspicuous.
          6 Phyllaries 25-125 in 3-9 series; receptacles flat or slightly convex
          6 Phyllaries 6-25 (-60) in 2-3 series; receptacles globose.
             7 Stems not winged
1 Disc flowers pink, purple, or white
               8 Receptacle paleate
               8 Receptacle epaleate.
                 9 Disc flowers 1-5 (rarely more) per head.
                   10 Disc flowers white (rarely cream), 3; heads not aggregated into a secondary cluster subtended by bracts; [se. TX]
                   10 Disc flowers lavender to purple, sometimes so lightly so as to be white, 1-4 (-5+); heads aggregated into clusters of 1-40 heads, subtended by 1-3 bracts; [collectively widespread in our region]
                     11 Heads (1-) 10-40 per secondary cluster, borne in corymbiform arrays; bracts subtending clusters (2-) 3, deltate; pappus of 5 (-6) scales, each aristate
                     11 Heads 1-5+ per secondary cluster, borne in spiciform arrays; bracts subtending clusters 1-2, linear, lanceolate, or spatulate; pappus of 6-10 scales, laciniate or aristate
                 9 Disc flowers (2-) 10-100+ per head (at least most heads with >10 flowers).
                       12 Phyllaries 5-15 (-21) in 1-2 (-3) series.
                          13 Involucres 2-3 mm in diameter; flowers 7-10 per head; [Coastal Plain, FL and GA]
                          13 Involucres 4-15+ mm in diameter; flowers 20-80 per head; [SC, GA, and FL westwards]
                       12 Phyllaries 18-many in 5+ series.
                            14 Phyllary tips modified into a spine or into an enlarged, lacerate or pectinate network or fringe; receptacle epaleate, but densely bristly; [tribe Cynareae].
                              15 Heads discoid, all flowers similar
                                16 Pappus normally of plumose bristles (and keyed elsewhere), but sometimes reduced to scales or awns
                                16 Pappus of an outer setiform scales (appearing as "flattened bristles"
                              15 Heads disciform or radiant, the outer flowers of the head sterile, with long lobes, appearing like false rays
                                  17 Plant a perennial; flowers pink to purple, flowering Jun-Oct
                                  17 Plant an annual; flowers pale to medium blue, flowering Apr-Jun
                            14 Phyllary tips not so modified, unarmed and unelaborate; receptacle epaleate and naked; [tribe Vernonieae].
                                    18 Peripheral flowers of the heads enlarged and bilaterally symmetrical, appearing like "false rays"
                                    18 Peripheral flowers of the heads similar to the interior flowers, all disc flowers.
                                       19 Annuals; cypselas not ribbed
                                       19 Perennials; cypselas 8-10-ribbed.
image of plant
Show caption*© Jacek Pietruszewski, some rights reserved (CC BY), uploaded by Jacek Pietruszewski
                                         20 Heads each subtended by 3-8 leafy bracts; pappus of narrow scales only, quickly falling
                                         20 Heads not subtended by leafy bracts; pappus of an inner series of scales or bristles and an outer series of bristles, persistent
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