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Keyed in multiple places:

Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

Key to Asteraceae, Key B: herbaceous composites with opposite or whorled leaves
and discoid or disciform heads (lacking ray florets)

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image of plant
Show caption*© Scott Ward, some rights reserved (CC BY), uploaded by Scott Ward
1 Pappus present, of 5-60 barbellate bristles; receptacle naked (without paleae or well-developed bristles); [tribe Heliantheae; subtribe Eupatoriae].
  2 Plant a twining herb, phyllaries and disk florets 4 per head
  2 Plant stiffly erect to sprawling but never twining, phyllaries and disk florets usually > 4 per head.
    3 Leaves in whorls of 3-7, > 2 cm wide
    3 Leaves opposite, rarely alternate or whorled, if whorled, < 2 cm wide.
      4 Cypselae rostrate (with long beaks); the achene portion not bearing ribs
      4 Cypselae not beaked, the achene variously ribbed.
        5 Achenes (and ovaries) 8-10-ribbed; outer phyllaries longitudinally striate
        5 Achenes (and ovaries) (3-) 4-5-ribbed; outer phyllaries not noticeably longitudinally striate.
          6 Heads pink to blue.
             7 Phyllaries in 4-6+ series, deciduous
             7 Phyllaries in 2-4 series, persistent (or deciduous in Praxelis).
               8 Heads pink (rarely bluish); receptacles flat; florets 18-25 per head; leaves sometimes gland-dotted
               8 Heads blue; receptacles conic; florets 25-70 per head; leaves gland-dotted.
                 9 Bristles ca. 30; florets 35-70+; phyllaries ca. 25, subequal, persistent
                 9 Bristles ca. 40; florets 25-30; phyllaries 15-25, unequal, deciduous (absence apparent in fruit)
          6 Heads white to cream or, rarely, pale lilac.
                   10 Florets 3-7 per head
                   10 Florets at least 9 per head.
                     11 Phyllaries not strongly imbricate, with the principal ones subequal and sub-biseriate; petioles 0.5-10 cm
                     11 Phyllaries clearly imbricate, in 3+ series, the margins usually glandular; some species epetiolate
image of plant
Show caption*© Scott Ward, some rights reserved (CC BY), uploaded by Scott Ward
1 Pappus either absent, or of scales, setae, or awns; receptacle naked, paleate, or bearing bristles.
                       12 Leaves whorled, linear, < 2 mm wide; head solitary; [aquatic herb growing in shallow stagnant water]
                       12 Leaves opposite (or alternate in part), broader in shape and > 5 mm wide; heads typically not solitary; [terrestrial or wetland plants].
image of plant
Show caption*© Scott Ward
                          13 Receptacle naked (epaleate).
image of plant
Show caption*© Scott Ward
                            14 Pappus of 2-12 scales; heads white, pink, or blue (yellow in Schkuhria).
                              15 Heads with 20-125 florets; leaves serrate or ± dentate (at least distally); [rarely naturalized exotics or s. TX/FL natives]; [tribe Eupatorieae].
                                16 Leaves petiolate; corolla tube glabrous, typically blue or lavender colored (sometimes white tinged); heads with 20-125 florets; [naturalized exotics or s. FL native]
                                16 Leaves sessile; corolla tube glandular-pubescent, typically white colored (sometimes pink-purple tinged); heads with 75-125 florets; [s. TX native]
                              15 Heads with 10-30 florets (or fewer in Schkuhria); leaves entire; [natives, of FL, s. GA, MS, and TX in our area]; [tribe Heliantheae; subtribe Chaenactidinae].
                                  17 Leaves 3-5 lobed (or foliolate); cypselae with curled hairs (Florestina tripteris) or villous on angles (Schkuhria pinnata); [s. TX in our area or ne. waif].
                                    18 Heads discoid, corolla white; cypselae with curled hairs; [s. TX in our area]
                                    18 Heads discoid, sometimes with 1 (-2) diminuitive rays, corolla (of discs) yellow; cypselae villous, at least at bases or on angles; [waif of ne US, native in sw. US]
image of plant
Show caption*© Scott Ward
image of plant
Show caption*© Scott Ward
                                  17 Leaves simple or unlobed; cypselae with straight hairs; [variously distributed in s. GA and FL w. to MO and s. TX]
                            14 Pappus none, or of a few bristles or irregular coroniform lobes; heads green to yellow.
                                       19 Heads bright yellow, closely aggregated into corymbiform arrays of flat-topped to dome-shaped glomerules
                                       19 Heads greenish or greenish yellow, borne in spiciform, racemiform, or paniculiform arrays.
                                         20 Heads in paniculiform arrays, all or most of the heads not subtended by bracts
                                         20 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract
 Iva
                          13 Receptacle with paleae or well-developed bristles.
                                           21 Heads small, less than 1 cm in diameter at anthesis (the female heads enlarging in Xanthium); disc florets dull white or suffused with green or purple; florets mainly unisexual (either in the same heads and then males central and females peripheral, or in separate female and male heads); female florets 0-8 per head; [tribe Heliantheae; subtribe Ambrosiinae]
                                             22 Heads unisexual; cypselas shed within an indurated bur or “nut” with hooked or straight spines developed from the phyllaries and/or paleae.
                                               23 Involucre of the female heads with tubercles or straight spines developing from the phyllaries; burs 1-8 mm long
                                               23 Involucre of the female heads with hooked spines developing from the phyllaries/paleae; burs 10-35 mm long
                                             22 Heads bisexual, with functionally male and female flowers in the same head; cypselas shed individually, not enclosed.
                                                 24 Heads in paniculiform arrays, all or most of the heads not subtended by bracts
                                                 24 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract
 Iva
                                           21 Heads larger, mostly > 1 cm in diameter at anthesis; disc florets conspicuously white, yellow, pale yellow, or purple; florets mainly bisexual; female florets > 12 per head (except 2-8 in Polymnia and 8-15 in Verbesina occidentalis).
                                                    25 Leaves strongly basally disposed, the basal-most leaves sitting almost flat on the ground and overlapping; disc flowers maroon-purple
                                                    25 Leaves mainly or strictly cauline (not basally disposed); disc flowers white, yellow, or reddish-brown.
                                                      26 Disc flowers bright yellow or reddish-brown.
                                                        27 Involucre of phyllaries subtended by a calyculus of bracts obviously different in color, texture, and shape than the phyllaries.
image of plant
Show caption*© Paul Marcum
image of plant
Show caption*© Alan M. Cressler
                                                          28 Phyllaries usually distinct, rarely connate proximally; disk florets bright yellow
                                                          28 Phyllaries connate (both proximally-distally connate); disk florets yellow to reddish-brown
image of plant
Show caption*© Jay Horn
                                                        27 Involucre of phyllaries not subtended by a calyculus (phyllaries sometimes in 2+ series, but without obvious calyculi below).
                                                            29 Plants erect; heads without ray florets; [wet pine savannas and bogs; FL panhandle]
                                                            29 Plants primarily prostrate or trailing, sometimes erect; heads with or without ray florets; [habitats various, widespread natives and non-natives]
                                                      26 Disc flowers bright white or pale yellow.
                                                              30 Stems not winged; plants erect or spreading.
                                                                 31 Cypselae 3-4 angled; pappus falling (of 2-12 awns or bristles); leaf margins irregularly crenate to serrate, the surfaces sometimes roughened but lacking glands; [e. of TX]
                                                                 31 Cypselae 5-ribbed; pappus absent; leaf margins entire or serrulate, the surfaces gland-dotted; [s. TX]
image of plant
Show caption*© Gary P. Fleming
                                                              30 Stems winged; plants erect.
                                                                   32 Disc flowers bright white; leaves unlobed or with 2 basal lobes
                                                                   32 Disc flowers creamy or pale yellow; leaves prominently pinnately lobed, with 5-many 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.
                            14 Leaf blades unlobed.
                              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.
                                16 Involucres 8-20+ mm in diameter; cypselae 1.5-4.5 mm long
                                16 Involucres (3-) 5-8 (-10) mm in diameter; cypselae 1.5-2 mm long
                            14 Leaf blades 1-3× pinnately or palmately lobed into linear or spatulate segments.
                                  17 Annual 0.1-5 dm tall.
                                    18 Disc corollas cream to pale yellow, 0.5-0.8 mm long; fresh plants malodorous; [waif]
                                    18 Disc corollas greenish yellow, 1.1-1.3 mm long; fresh plants pineapple-scented; [common weed, especially northwards in our region]
                                  17 Perennial, biennial or annual 4-15 dm tall.
                                       19 Heads borne in paniculiform, racemiform, or spiciform arrays, never flat-topped; flowers < 50 per head
                                       19 Heads borne in corymbiform arrays; flowers 60-300+ per head