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Keyed in multiple places:

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Key to Tanacetum

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1 Leaves simple, crenate (sometimes with a few basal lobes)
1 Leaves 1-3-pinnatifid.
  2 Rays present, white (T. parthenium) or pink-red colored; leaf blades 4-10 cm long, 1-2-pinnate (with 3-5 pairs of primary lobes)
    3 Rays pink to red-colored; [waif, PA]
    3 Rays white; [scattered throughout e. US]
  2 Rays absent (rarely present and very small, and then yellow); leaf blades 8-20 cm long, 2-3-pinnate (with 4-20+ pairs of primary lobes)

Key to Asteraceae, Key G: Herbaceous composites with the leaves alternate, the heads lacking rays, and with 0 pappus

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1 Receptacle paleate (bearing receptacular bracts which individually subtend at least some of the flowers of the head).
  2 Involucres absent or vestigial, usually with 0 phyllaries; heads very small, < 6 mm high, < 4 mm wide; annuals, < 4 dm tall; disc corollas hidden or dingy in color; [tribe Gnaphalieae]
    3 Bisexual flowers (1-) 2-10 (-11), pappus of (11-) 13-28+ bristles visible in heads; functionally staminate flowers 0.
      4 Receptacles cylindric to clavate (5-15× as tall as the diameter); most pistillate paleae open to ± folded (at most each enfolding, not enclosing a floret; apices acuminate to aristate); innermost paleae erect to ascending in fruit; cypselae mono- morphic (the outer ± equaling the inner)
      4 Receptacles fungiform to obovoid (0.4-1.6× as tall as the diameter); most pistillate paleae ± saccate, each ± enclosing a floret, apices blunt; innermost paleae spreading in fruit; cypselae dimorphic (the outer longer than the inner)
    3 Bisexual flowers 0 or 2-7, pappi 0; functionally staminate flowers 0 or 2-5, pappi 0 or of 1-10 (-13) bristles hidden in heads
        5 Paleae of the bisexual or staminate flowers flat to concave, not enclosing florets, apices entire; cypselae glabrous; [mainly west of the Mississippi River, rarely east (as in MS, AL, GA, and SC]
        5 Paleae of the bisexual flowers saccate, each enclosing a floret, apices 2-fid or 3-fid; cypselae (at least the outer) strigose; [se. Texas]
  2 Involucres present, conspicuous, of many phyllaries; heads larger, 2-20+ mm wide; perennials or coarse annuals, 2-25 dm tall; disc corollas apparent, yellow, white, or pink to purplish.
          6 Disc flowers yellow or greenish yellow; [either native of s. TX southwards, or a waif]
             7 Phyllary margins and tips scarious; fresh foliage aromatic
             7 Phyllary margins and tips herbaceous; fresh foliage not aromatic
          6 Disc flowers white or whitish to pink or purple; [collectively widespread].
               8 Heads in corymbiform arrays; heads bisexual; involucres not burlike or nutlike, lacking tubercles or hooked or straight prickles or spines; leaves lanceolate, unlobed, cuneate at base
                 9 Heads lacking ray flowers; disc flowers pink (rarely nearly white); [Coastal Plain; FL and GA]
                 9 Heads with 5 white (fading to cream), scoop-shaped, inconspicuous ray flowers (keyed here as a 'failsafe'); disc flowers white; [widespread in our region]
               8 Heads in spiciform or racemiform arrays; heads unisexual (each head either with only female or only male flowers); involucres burlike, with tubercles or straight or hooked spines or prickles; leaves ovate or broader (in outline), often pinnatifid or bipinnatifid, truncate, cordate, or cuneate at base; [collectively widespread in our region].
                   10 Involucres of pistillate heads (burs) 1-4 mm long, with (1-) 5-12+ straight spines; larger leaves bipinnatifid
                   10 Involucres of pistillate heads (burs) 10-40 mm long, with 30-75+ hooked prickles; phyllaries larger leaves pinnatifid or unlobed
1 Receptacle epaleate (lacking receptacular bracts individually subtending flowers, but the receptacle sometimes bearing bristles, setae, hairs, or pits with laciniate margins.
                     11 Flowers white, pink, purple, or bluish.
                       12 Annuals, (1-) 2-10 (-30+) cm tall; corollas whitish, inconspicuous, absent on most of the (pistillate) flowers; leaves 2-3× pinnati-palmately lobed into linear segments; cypselae with an apical spine
                       12 Perennials, 10-150 cm tall; corollas at least light pink and often darker pink, purple, or blue, conspicuous, present on all flowers; leaves pinnately lobed or entire, the segments not linear; cypselae not spined.
                          13 Heads ovoid, 10-21 mm long; flowers 15-40 mm long, with long, narrow lobes; phyllaries >30, in 6+ series, and the apices often with a fringe of appendages and/or a spine tip; basal and lower stem leaves usually pinnately lobed (to entire and unlobed); [widespread in our region, especially northwards]
                          13 Heads cylindrical, 2-6 mm long; flowers ca. 3 mm long, with deltate lobes; phyllaries 12-15 in 2-3 series, herbaceous and unadorned; basal and lower stem leaves entire and unlobed; [Coastal Plain of FL and GA]
                     11 Flowers yellow, cream, or rarely red-tinged.
                              15 Heads 3-4 (-6) mm in diameter, solitary; plants 0.3-3 dm tall; [ballast waif, especially in wet, saline places]
                              15 Heads (3-) 5-20+ mm in diameter, solitary or borne in corymbiform or paniculiform arrays; plants 1.5-15 dm tall.
                                    18 Disc corollas greenish yellow, 1.1-1.3 mm long; fresh plants pineapple-scented; [common weed, especially northwards in our region]
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