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Key to Symphyotrichum

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1 Basal and lower stem leaves petiolate, with blades cordate to rounded at the base; [subg. Symphyotrichum, sect. Symphyotrichum, subsect. Heterophylli]
1 Basal and lower stem leaves sessile (often cordate-clasping), or if petiolate then with cuneate to attenuate bases.
  2 Vegetative parts (stems, leaves, array branches, phyllaries) persistently bluish-glaucous; leaves slightly fleshy in texture and clasping; plants nearly glabrous (leaf margins scabrous, rarely upper stems somewhat hirsute); stems 2-7 (-12) dm tall; [subgenus Symphyotrichum, section Symphyotrichum, subsection Heterophylli, series Concinni].
  2 Vegetative parts (stems, leaves, array branches, phyllaries) green, not bluish-glaucous; leaves mostly not fleshy (except subg. Astropolium); plants glabrous or variously hairy; stems 2-30 dm tall.
    3 Leaves strongly basally disposed, basal leaves linear, upper cauline leaves much reduced; heads few, long-pedunculate (peduncles 1-20+ cm) in open ± corymbiform arrays; disc florets 47-57; [of wet pine savannahs of FL and s. AL]; [subgenus Chapmaniani].
    3 Leaves cauline, basal and proximal leaves generally not linear, often withered by anthesis; heads few to many, mostly in paniculiform or racemiform arrays; disc florets often fewer; [collectively widespread].
      4 Ray florets mostly in 2-3 series, blades 1.3-4.2 mm, often not exceeding mature pappus (S. tenuifolium and S. bracei in 1 series to 8.5 mm); plants appearing entirely glabrous (leaf axils or margins sometimes inconspicuously strigillose); plants either taprooted annuals or perennials with succulent, linear, entire leaves; [coastal wetlands, often saline, or disturbed areas inland]; [subgenus Astropolium]
        5 Leaves succulent, linear (1-6 mm wide) and entire; ray laminae (4.5-) 5-8.5 (-9) mm, in a single series; plants perennial, heads (1-) 3-20 (-40).
        5 Leaves not succulent, usually broader or toothed; ray laminae 1.3-4.2 mm, usually in 2-3 series (laminae 3.7-7 mm and in 1 series in S. divaricatum); plants annual, often copiously branched, heads (10-) 30-100 (-150+).
      4 Ray florets in 1 series, mostly >4mm; stems usually pubescent at least in lines distally, leaves often pubescent or scabrous; plants perennials from crowns, caudices, or rhizomes, leaves not succulent; [various habitats, rarely saline].
          6 Stem leaves sessile, entire, and cordate- or auriculate-clasping at base (if only rounded or cuneate, then mostly 1-3 cm long); leaves crowded, internodes of main stem < 3.5 cm long (rarely longer in S. patens); plants stipitate-glandular in arrays (on upper stems, leaves, peduncles, bracts, and/or phyllaries; absent in sect. Concolores and sparse to absent in some vars. of S. patens); rays purple, blue, or lavender; [subgenus Virgulus]
          6 Stem leaves winged-petiolate (lower, often withering by anthesis) to sessile (upper), often toothed, bases attenuate to auriculate-clasping (main stem leaves mostly > 3 cm long); leaves not crowded, internodes of main stem > 3.5 cm long; arrays eglandular; rays white in some species.
             7 Phyllary tips widely spreading or recurved, usually either involute or foliaceous, faces glabrous or variously pubescent.
               8 Phyllary apices spinose, either tightly involute or tipped with a white spine; flowers white (except S. kentuckiense).
                 9 Free tips of phyllaries flat, tipped with a white spine (otherwise acute); stem leaves crowded (internodes mostly <1 cm), linear or oblong, 1-4 mm wide, usually upcurved; [subgenus Virgulus, section Ericoidei]
               8 Phyllary tips acute to acuminate, flat; flowers pink, purple, or lavender (rarely white in S. firmum).
                   10 Upper stems, peduncles, bracts, and phyllaries ±densely hirtellous and usually also stipitate-glandular; leaves entire, sessile, and mostly rounded to subclasping at base; [subgenus Virgulus]
                     11 Involucres turbinate, phyllaries in 6-9 series; ray laminae 12-20 mm long, pink to purple; peduncles (1-) 4-10 (-25) cm with numerous (8-15) appressed, linear-oblong bracts 1.5-4mm; stem leaves lacking axillary clusters; [subgenus Symphyotrichum, section Turbinellum]
                     11 Involucres campanulate to cylindric, phyllaries in 3-6 series; ray laminae 3-11 (-14) mm long (longer in S. boreale); peduncles not as above (except S. dumosum and S. estesii); stem leaves with or without axillary clusters

Key to Symphyotrichum, Key A: perennial asters with petiolate, cordate-bladed lower leaves
[of subgenus Symphyotrichum, sections Heterophylli and Concinni]

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1 Phyllary tips squarrose, or spreading and foliaceous; heads larger: involucre 5-10 mm high; disc flowers 33-50 (or more); ray flowers (13-) 20-45.
  2 Phyllaries linear, in 4-7 series; disc flowers 4.0-5.5 mm long; [dry, rocky soils of open woodlands and prairies; IL and n. MO south through MO and se. KS to s. AR and se. OK]
  2 Phyllaries broadly lanceolate, foliaceous, in 3-5 series; disc flowers 5.8-6.8 mm long; [moist forests of the higher-elevation Southern Appalachians; w. NC and e. TN south to nw. SC and n. GA]
1 Phyllary tips appressed or ascending; heads smaller: involucres 3.8-7(-8) mm high; disc flowers (8-) 10-25 (-30); ray flowers 8-20 (-25).
    3 Leaves glaucous, slightly fleshy, glabrous on both faces; stems and array branches nearly glabrous; [series Concinni]
    3 Leaves not glaucous, herbaceous in texture; stems and array branches densely pubescent to glabrate.
      4 Leaves entire to weakly undulate or crenate-serrate, typically narrowly lanceolate or linear-lanceolate at midstem; phyllaries with a short diamond-shaped green blaze (1-1.5× as long as wide).
        5 Stem leaves nearly all distinctly petiolate, petioles scarcely winged, blade bases cordate to subcordate; leaves glabrous adaxially except on veins.
        5 Stem leaves usually sessile above, cuneate and gradually narrowed onto petiole and/or petiole wings dilated at bases; leaves usually scabrous or pubescent adaxially.
          6 At least some cauline leaves with petiole wings dilated to cordate-clasping bases (often panduriform); cauline leaf blades ovate to lanceolate, bases cordate to broadly cuneate, upper sessile and clasping; upper stems and often adaxial leaf surfaces densely hirtellous with whitish hairs
          6 Petioles not notably dilated at the base; mid and upper cauline blades narrowly lanceolate to linear, bases cuneate to attenuate, gradually narrowed onto the petiole or sessile; upper stems minutely strigillose or pilosulous, rarely glabrous; [series Concinni].
             7 Cauline leaves narrowly lanceolate; basal leaves cordate; inflorescence denser, rays blue or purple, sometimes pale; [MN, NY, and ON south to TN and AR]
             7 Cauline leaves (except lowermost) linear or linear-lanceolate; basal leaves often rounded or cuneate; inflorescence sparse, heads often long-pedunculate with white rays; [West Gulf Coastal Plain, apparently disjunct eastwards in MS and AL]
      4 Leaves regularly serrate or crenate-serrate (uppermost sometimes entire), mostly broader; phyllary green blazes lanceolate to linear (> 2× as long as wide; except S. lowrieanum and S. schistosum).
               8 Rays white (rarely pale lilac); phyllary green zones not broadened towards tip, linear-lanceolate to linear (> 4× as long as wide), apices long-acuminate and ascending; inflorescence usually densely racemose, the branches stiffly erect; stems glabrate or sparsely pilose distally
               8 Rays bluish or purplish (rarely white); phyllary green zones diamond-shaped to lanceolate (< 4× as long as wide; the inner may be linear-lanceolate in S. drummondii), apices various; inflorescence usually diffusely paniculiform, branches spreading to ascending.
                 9 Stems densely pubescent distally and in arrays; phyllary green zones lanceolate to linear-lanceolate.
                 9 Stems glabrate or distally sparsely pubescent; phyllary green zones diamond-shaped to lanceolate (1-3× as long as wide).
                       12 Basal and proximal leaves deeply cordate; petioles narrowly winged; leaf blades usually pilose abaxially
                       12 Basal and proximal leaves shallowly cordate to rounded; petioles broadly winged, wings expanded near blade; leaf blades usually glabrous, sometimes thinly glaucous.
                          13 Plants solitary or several-stemmed; [more widespread]

Key to Symphyotrichum, Key B: perennial salt-marsh asters
[of subgenus Astropolium] (clone)

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1 Midstem leaves (1.0-) 1.5-2.7 mm wide; involucres 4.1-5.3 mm high; ray flowers 10-16; disc flowers (10-) 13-23; achenes 1.5-2.0 (-2.5) mm long; pappus 3.0-4.4 mm long; [of FL southward]
1 Midstem leaves (1.5-) 3-6 mm wide; involucres 6-9.5 (-11) mm high; ray flowers (12-) 17-25; disc flowers 25-45 (-54); achenes 2.8-4.0 (-4.5) mm long; pappus 5.0-6.1 mm long; [widespread in our area]

Key to Symphyotrichum, Key C: annual salt-marsh asters
[of subgenus Astropolium]

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1 Heads usually dense in an elongate, pyramidal-paniculate arrangement; inner phyllaries 6-7 mm long, phyllary apices linear-acuminate, distal margins often inrolled/involute, green zone of phyllaries narrowly lanceolate, usually extending the entire length of the phyllary, chartaceous bases short or absent; pappus accrescent, 4-5.5 mm long at maturity and usually longer than coiled ray corollas; [habitats wet, saline]
1 Heads corymbiform to thyrsiform, diffusely paniculate, or secund to subsecund and paniculiform arrangements or at the tips of long, bracteate branches; inner phyllaries 4-6.5 mm long, phyllary apices acute to acuminate, distal margins inrolled/involute or not, green zone of phyllaries lanceolate to elliptic, chartaceous bases usually conspicuous; pappus not accrescent, 3.5-4 (-5) mm long at maturity, longer or shorter than ray corollas; [habitats moist to wet, rarely saline].
  2 Phyllary tips appressed, acute, flat, inner phyllaries with broadly lanceolate, distinctly demarcated, apical green zone, proximal ½ -1/3 white-chartaceous; ray flower blades erect, often involute along the edges (curling inward lengthwise), rarely coiling back distally (if so, then only ca. 1/2 coil), usually shorter than mature pappus; disc flowers (3-) 7-14
  2 Phyllary tips loose, linear-acuminate, distal margins often inrolled/involute, inner phyllaries with narrowly lanceolate, often weakly demarcated apical green zone, white-chartaceous bases short, ca. 1/3-1/2 the length of the phyllaries; ray flower blades not involute along edges, usually coiling back distally in 1-4 or more coils, usually as long or longer than mature pappus; disc flowers either (6-) 8-15 or 11-23 or (20-) 33-45 (-50).
    3 Heads usually corymbiform to thyrsiform in arrangement (borne primarily on distal branches, distally clustered); inner phyllaries 4-5.5 (-6) mm long; phyllary apices acute to abruptly short-acuminate or long-acuminate, the distal margins inrolled/involute or not; ray flowers in 1 (-2) series, corollas 2-3 mm long, the blades 0.1-0.3 mm wide (dried), white to light pinkish or slightly blue, coiling back in 1-2 coils or less commonly remaining straight; disc flowers (6-) 8-15; [peninsular FL to s. AL]
    3 Heads diffusely paniculiform to pyramidal-paniculiform to corymbiform or second to subsecund and paniculiform; inner phyllaries 5-6.5 mm long; phyllary apices long-acuminate, the distal margins usually inrolled/involute; ray flowers in 1-3 series, corollas 2-7 mm long, the blades 0.2-0.8 mm wide (dried), white to blue or purple, coiling back in 2-5 coils; disc flowers either 11-23 or (20-) 33-45 (-50).
      4 Heads at first at ends of long, bracteate branches, then produced and maturing as axillary and nearly sessile or on very short lateral branches, commonly on one side of the main stem and appearing secund to subsecund, in paniculiform arrangements; ray flowers in 2-3 series, corollas mostly 2-3.5 (-4) mm long, the blades 0.2-0.4 mm wide (dry), blue to purple, coiling back in 2-3 (-4) coils; disc flowers 11-23; [e. GA s. to s. FL, w. to LA]
      4 Heads often at ends of long, bracteate branches, axillary heads usually maturing on elongate lateral branches, the whole arrangement often diffusely paniculiform to pyramidal-paniculiform, or heads more distally disposed and the arrangement corymbiform to thyrsiform; ray flowers in 1 series, corollas mostly 4-7 mm long, the blades 0.4-0.8 mm wide (dry), blue to white, coiling back in 3-5 coils; disc flowers (20-) 33-45 (-50); [sc. U.S. east to AL and scattered eastward as an introduction]

Key to Symphyotrichum, Key D: perennial asters [of subgenus Virgulus]

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1 Mid and upper stem leaves > 8× as long as wide; phyllaries tipped with a small, white spine; rays white (to pale pink); involucre 2.5-4.5 (-5) mm high; disc flowers 6-12 (-20) per head; [section Ericoidi]
1 Mid and upper stem leaves 2-7× as long as wide; phyllaries not spine-tipped; rays purple, lavender, rose, blue (rarely nearly white); involucre > 5 mm high (except sometimes as short as 4 mm high in S. adnatum of s. GA and FL west to LA); disc flowers (6-) 11-110 per head.
  2 Stem leaves 0.1-1(-1.3)cm long, either ascending-appressed, appearing adnate to stem, or triangular and deflexed; [of the Coastal Plain]; [section Patentes, series Brachyphylli].
    3 Blades of mid-stem leaves ascending-appressed, basally decurrent; [of s. GA south to s. FL, west to se. LA]
    3 Blades of mid-stem leaves spreading, the apical portion then abruptly deflexed, basally clasping; [of e. NC to c. peninsular FL]
  2 Stem leaves mostly ≥1.5 cm long, spreading to erect-ascending; [collectively widespread].
      4 Midstem leaves <3cm long, bases rounded to cuneate (sometimes subclasping); leaves and bracts silvery-sericeous (glabrous in S. concolor var. devestitum); leaves held erect-ascending, lower often twisted by 90 degrees to bring edge in line with stem; plants not stipitate-glandular; [section Virgulus].
        5 Bracts large, leafy, concealing involucres; plants branched; inflorescences open, involucres mostly terminal or clustered at ends of branches; rays 13-36; cypselas glabrous.
          6 Phyllaries with lower (outer) surfaces glabrous to glabrate (rarely sparsely to densely sericeous), the margins ciliate with thick-based, spreading hairs 0.5-1.0 mm long (much longer than those of the surfaces); largest phyllaries with terminal, green, pubescent portion 2/3-3/4 as long as the total phyllary length (longer than the proximal, indurated, glabrate portion); middle phyllaries mostly > 8 mm long and > 2.5 mm wide, averaging 9 (-14) mm long × 3 (-5) mm wide; involucre 8-15 mm tall; [mostly of the West Gulf Coastal Plain, disjunct e. to VA and s. GA]
          6 Phyllaries densely sericeous, the vestiture of the margins similar to that of the surfaces; largest phyllaries with terminal, green, pubescent portion 1/4-1/3 (-1/2) as long as the total phyllary length (shorter than the proximal, indurated, glabrate portion); middle phyllaries mostly < 7 mm long and < 2 mm wide, averaging 6 mm long × 2 mm wide; involucre 7-11 mm tall; [mostly of the Great Plains, s. to ne. TX, nw. AR, and s. IL]
        5 Peduncle bracts abruptly reduced, appressed, not concealing involucres; inflorescences racemose, sometimes subsecund, stems sparingly branched or unbranched; rays 7-16; cypselas densely strigose.
             7 Phyllaries long-acuminate, spreading to recurved; phyllaries with woolly, tangled hairs; involucre 7-9 mm tall; [c. FL Panhandle]
             7 Phyllaries acute, appressed; phyllaries either with appressed, straight hairs (moderately to densely sericeous) or glabrous to sparsely pilose; involucre 5-7 mm high; [collectively widespread].
               8 Phyllaries and upper stem leaves moderately to densely sericeous (silky-pubescent); [widespread]
               8 Phyllaries and upper stem leaves glabrous or sparsely pilose; [of the Gulf Coastal Plain]
      4 Midstem leaves >3cm, bases strongly cordate- or auriculate-clasping or subclasping to cuneate; leaves and bracts scabrous, strigoso-scabrous, or hirtellous; main stem leaves spreading or lax, not twisted; plants stipitate-glandular in arrays (glands sparse in S. fontinale and S. estesii; sometimes absent in S. patens).
                 9 Mid-stem leaves cuneate, rounded, or subclasping; [section Grandiflori].
                   10 Phyllaries appressed; phyllary faces glabrous or glabrate, lacking stipitate glands (though there may be a few stipitate glands on the phyllary margins); heads 6-7.6 mm high.
                     11 Involucres 5.0-6.4 mm high; rays white; [of wet prairies in the Eastern Highland Rim of TN]
                     11 Involucres 6.0-7.6 mm high; rays pale pink, bluish, or violet; [of wet pinelands and marshes of e. Panhandle FL south to s. FL]
                   10 Phyllaries spreading, squarrose, or reflexed; phyllary faces moderately to densely stipitate-glandular (and also often pubescent or scabrous with non-stipitate hairs); heads (5-) 7-12 (-15) mm high; [of dry habitats, of mainly inland provinces, though extending to the Coastal Plain in e. VA, e. NC, and nc. SC].
                       12 Involucres 8.5-12 (-15) mm high; phyllaries scabrous and stipitate-glandular; lower stem leaves (often withered by flowering season) cordate-clasping; [of acidic habitats of the Coastal Plain and Piedmont of e. and c. VA south through e. and c. NC to nc. SC]
                       12 Involucres 4-9 mm high; phyllaries pubescent and stipitate-glandular; lower stem leaves cuneate, rounded, or subclasping; [of calcareous habitats, south to sc. VA, w. NC, nc. AL, n. MS]
                          13 Upper stems, leaves, bracts, and outer phyllaries lacking stipitate glands, inner phyllaries densely stipitate-glandular; involucres (5-)30-150+, 4-6mm high; [interserial hybrid]
                          13 Upper stems, leaves, bracts, and phyllaries usually stipitate-glandular (also hirtellous); involucres 1-30(-70), (5-) 7-9mm high
                            14 Phyllaries with attenuate, loosely spreading tips; disc flowers 50-110; ray flowers (40-) 50-75 (-100); [section Polyliguli]
                            14 Phyllaries with obtuse to acute tips (the inner phyllaries sometimes acuminate, but not attenuate); disc flowers 15-50; ray flowers 9-24 (-30); [section Patentes, series Patentes]
                              15 Involucres 8-10 (-12) mm high; disc flowers 8-10 mm long, white with purplish lobes; heads 4-5 (-6) cm across (ray tip to ray tip), the rays 14-24 mm long; plants strongly rhizomatous, forming clonal colonies with the stems mostly scattered along the rhizome (new stems typically arising at least several cm from the old ones); achenes 2.5-4.0 mm long, pale gray-brown, the trichomes about 0.4 mm long and distributed on and between the ribs; anthers purplish; pollen white
                              15 Involucres 5.5-7.5 (-8.5) mm high (or to 12 mm high in S. patens var patentissimum, barely entering our area in w. KY and w. MS); disc flowers 5.5-8 mm long, either white with purplish lobes or bright yellow; heads 3-4 (-4.5) cm across (ray tip to ray tip), the rays 10-18 (-20) mm long; plants cespitose, generally with 1 or more stems arising from caudices (the new stems arising near the old); achenes 2.0-4.0 mm long, tan, gray, brown, dark-brown, or black, the trichomes various (see below); anthers purplish or yellow; pollen white or yellow.
                                16 Disc flowers white with purplish lobes; stem leaves 7.5-12.5 (-14) cm long, thin in texture, soft-pubescent, the venation apparent, rugose-veiny and wrinkled; anthers purplish; pollen white; achenes 2.5-4.0 mm long, the trichomes concentrated on the ribs, < 0.4 mm long, appressed; [primarily of the Mountains, less commonly the Piedmont, mostly in moist, shady to semi-sunny situations]
                                16 Disc flowers bright yellow; stem leaves (2-) 3-7 (-9) cm long, thick in texture, scabrous, the venation inconspicuous; anthers yellow; pollen yellow; achenes 2.0-3.5 mm long, the trichomes distributed on and between the ribs, mostly > 0.4 mm long, spreading; [collectively widespread in our area, mostly in dry, semi-sunny to sunny situations]
                                  17 Involucres broadly turbinate, mostly 8-12 mm long; phyllaries in 4-7 series (grading into bracts), more or less appressed, obtuse to acute, middle ones 1.2-1.7 mm wide (ovate to lanceolate), densely strigillose or sericeous-strigose; plants largely eglandular (except for sparse sessile glands on phyllaries), usually with leaves only ca. 2-3 cm long at mid-stem, developing many long stiff branches with abrupt further reduction in leaf size; [from w. KY and w. MS westward]
                                  17 Involucres campanulate or narrowly turbinate, mostly 5-7.5 mm long; phyllaries in 4-5 (-6) series, often somewhat squarrose, acute to acuminate, middle ones 0.7-1.2 mm wide (linear to lanceolate), densely strigillose to almost glabrous; plants glandular (mostly stipitate-) or largely eglandular, with varied leaf size and branching; [collectively widespread].
                                    18 Mid-stem leaves mostly 5-7 cm long, separated by internodes of (1-) 1.5-3 (-4) cm at their densest, usually spreading; plants usually 0.8-1.6 m tall; heads mostly 9-12 mm wide
                                    18 Mid-stem leaves mostly 3-5 cm long, separated by internodes of (0.5-) 1-2 (-3) cm at their densest, often adnate-ascending; plants usually 0.4-0.8 m tall; heads mostly 7-11 mm wide.
                                       19 Stems and leaves generally eglandular (except sometimes for scattered glands on distal branches), but with dense ascending eglandular hairs; plants usually dull greyish-green, not much darkening when dried; leaves usually with gradual or irregular reduction from base of stem to summit; mid-stem leaves with length/width (2-) 2.5-4 (-4.5), not forming a distinct overlapping cluster; bracts on proximal thirds of peduncles mostly 2-3 (-5) mm wide
                                       19 Stems and leaves with dense to sparse stipitate-glands, with or without eglandular hairs; plants somewhat bluish-waxy, often becoming blackish when dried; leaves abruptly reduced in size with each branching order; mid-stem leaves [directly below inflorescence] with length/width (1.5-) 2-2.5(-3), clustered and overlapping along 10-20 cm; bracts on proximal thirds of peduncles mostly 1-2 (-3) mm wide

Key to Symphyotrichum, Key E: perennial asters with clasping or sheathing leaves
[of subgenus Symphyotrichum, sections Symphyotrichum and Concinni]

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1 Mid-stem leaves narrowed above the clasping base to an elongate petiolar portion (1/2-1/8 of the blade length) which flares abruptly into an ovate to lanceolate upper portion 10-55 mm wide; stem slightly to strongly zigzag in the upper portion; [series Punicei]
1 Mid-stem leaves linear to lanceolate; stem usually straight (lacking bends alternating at the nodes).
  2 Phyllaries appressed, apices acute to acuminate (also keyed in Key F); plants 1.5-4 (-6) dm; [ultramafic outcrop barrens, Clay co., NC]; [series Punicei]
  2 Phyllaries spreading; plants (1.7-) 6-25+ dm; [other habitats, collectively widespread].
    3 Phyllaries mostly obtuse to acute, sometimes acuminate, green zones foliaceous; mid and upper stem leaves mostly lanceolate or oblanceolate to linear, faces glabrous, bases slightly auriculate-clasping to short-petiolate and attenuate; stems sparsely hairy in lines above, otherwise glabrous; [series Symphyotrichum].
      4 Lower stem leaves distinctly petiolate, blades often with rounded bases; stems often flexuous; [moist forests; w. NC and e. TN south to n. GA].
      4 Lower stem leaves attenuate, sessile to winged-petiolate; leaves thick-textured, often slightly fleshy; stems erect; [marshes, pine savannahs; Atlantic Coastal Plain of GA northwards, disjunct in w. NC]
        5 Leaves linear, > 10× as long as wide; leaf bases only subclasping
    3 Phyllaries mostly long-acuminate to caudate; mid and upper stem leaves mostly ovate, obovate, lanceolate, or oblanceolate, scabrous adaxially (except S. firmum), bases strongly auriculate-clasping (except S. elliottii); stems densely hispid to sparsely hairy in lines; [series Punicei].
          6 Stem leaves cuneate or rounded at base; leaves thick, firm
          6 Stem leaves strongly auriculate-clasping; leaves membranaceous.
             7 Stems glabrous, occasionally hispidulous in lines; abaxial cauline leaf midvein glabrous; capitulescence dense, leafy; heads with white to pale lavender ray florets; shoots arising singly from elongate rhizomes
             7 Stems densely pubescent, usually purplish; abaxial cauline leaf midvein moderately to densely pubescent; capitulescence widely spreading and heads with lavender to purple ray florets; shoots often found in clumps of 2-6 arising from a persistent stout caudex
               8 Upper and lower leaf surfaces nearly the same color; upper stem leaves smaller in size than the midstem leaves
               8 Upper and lower leaf surfaces distinctly different in color (the lower pale green, the upper dark green); upper stem leaves (on branches leading to heads) equal or nearly so in size to mid-stem leaves
                 9 Plants to 6 dm tall; {other characters}; [nw. NC]
                 9 Plants 10-30 dm tall; {other characters}; [widespread]

Key to Symphyotrichum, Key F: perennial asters with involute phyllaries
[of subgenus Symphyotrichum, section Dumosi, subsection Porteriani]

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1 Ray flower blades (7-) 9-15 (-19) mm long, blue-violet (rarely white); involucres (4.5-) 5.5-7.1 (-8.5) mm high; [calcareous habitats, especially glades]
1 Ray flower blades (3-) 3.8-7.5 (-11) mm long, white (rarely slightly blue or violet); involucres (2.5-) 3.1-5.1 (-6.5) mm high; [various habitats, including glades].
  2 Disc flowers (13-) 17-39 (-67); ray flowers (10-) 16-28 (-38); involucres (2.5-) 3.5-5.1 (-6.5) mm high.
    3 Stems sparsely to densely hirsute; leaves pilose
  2 Disc flowers 5-17 (-28); ray flowers 7-17 (-23); involucres (2.7-) 3.1-4.1 (-4.9) mm high.
      4 Stems glabrous or glabrate; plants 1-4 (-5) dm tall; upper stem leaves lacking axillary fascicle shoots; [serpentine and diabase barrens of Piedmont of e. PA, e. MD, and nc. NC]
      4 Stems sparsely to densely hairy with short pubescence; plants 3-10 dm tall; upper stem leaves with axillary fascicle shoots; [prairies, woodlands, barrens, and glades of n. IL and n. IA south to n. AR and ne. OK]

Key to Symphyotrichum, Key G: perennial asters
[of subgenus Symphyotrichum, section Dumosi, subsections Divergentes and Dumosi]

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1 Mid and upper stem leaves mostly linear or linear-lanceolate, nearly parallel-sided or narrowed from near strongly auriculate-clasping base; ray blades (7-) 10-15 (-20) mm; stems and leaf faces glabrous
1 Mid and upper stem leaves elliptic to linear, cuneate or attenuate at base (auriculate-clasping but broader in S. rhiannon, rarely subclasping in other species); ray blades 3-11 (-13) mm; stems and leaf faces glabrous or pubescent.
  2 Plants annuals, from a taproot, glabrous; involucres narrowly turbinate or cylindro-turbinate (in bloom, broadened from peduncle to apex); inflorescence open and diffuse, bracts subulate, appressed-ascending, and inconspicuous; stem leaves attenuate with strongly sheathing petioles; [subgenus Astropolium]
  2 Plants perennials, rhizomatous or from branched caudices, usually pubescent at least in lines on stems or along leaf veins; involucres more or less campanulate (contracted above middle, less commonly cylindric); inflorescence various, bracts foliaceous (subulate in some forms of S. dumosum); stem leaves sheathing or not.
    3 Stem leaves (below arrays) oblanceolate-elliptic or oblong-lanceolate, auriculate-clasping; inflorescences open, sparsely bracteate (bracts mostly 1-3 per peduncle, foliaceous), leaves and bracts much reduced in arrays; plants 1.5-4 (-6) dm tall; [ultramafic outcrop barrens, Clay co., NC]; [subsection Symphyotrichum, series Punicei]
    3 Stem leaves various, not auriculate clasping; inflorescences leafy, often crowded, leaves and bracts gradually reduced (or bracts abruptly reduced, but 5-15+ per peduncle); plants (0.5-) 3-15 dm tall; [widespread in a variety of habitats]
      4 Peduncles long (usually many on plant > 2 cm long), with copious (5-15+) small, closely-spaced, oblong or linear-subulate bracts mostly 1-4 mm long, abruptly smaller than the stem and branch leaves; plants single or somewhat cespitose (rhizomes short); phyllary apices acute to obtuse, green zones broadened near apex (oblanceolate or diamond-shaped).
        5 Leaves and bracts thin, lax; bracts usually gradually reduced, lower linear-elliptic, upper acicular; involucres (2.5-) 3.5-4.5 (-5.5) mm, cylindric
        5 Leaves and bracts thick, firm; bracts abruptly reduced from stem leaves, oblong to linear-subulate; involucres (3-) 4.5-6.3 mm, cylindro-campanulate.
          6 Upper stems and array branches moderately to densely hirtellous; adaxial faces of upper stem and branch leaves strigoso-scabrous; phyllaries and bracts usually prominently mucronate; plants usually sparsely stipitate-glandular in arrays; [May Prairie, TN]; [subgenus Virgulus]
          6 Upper stems and array branches strigose, mostly in lines; adaxial faces of upper stem and branch leaves glabrous to scabrous; plants eglandular; [widespread].
             7 Peduncle bracts, at least lower and middle, mostly spreading or reflexed, oblong to linear-oblong, obtuse to subacute (rarely abruptly mucronate)
               8 Cauline leaves 3-7 cm long; branches few; peduncles long; rays 14-17 (-20)
               8 Cauline leaves to 15 cm long; branches abundant; peduncles long, short, or absent; rays 13-25.
                 9 Stems glabrate; branches not crowded; most peduncles long, their bracts short and of ± uniform length and shape
                 9 Stems glabrate, puberulent, or strigose; branches crowded; most peduncles short to absent, their bracts not uniform, some long and narrow.
                   10 Stems sparsely and finely puberulent; inflorescence small and terminal; rays 13-16 (-20)
      4 Peduncles short (< 2 cm long), bracts gradually reduced, foliaceous; plants strongly colonial from creeping rhizomes (except S. lateriflorum and S. tradescantii); phyllary apices various, acuminate with longer or less distinct green zones in many species.
                     11 Upper stems, array branches, and both faces of leaves strigoso-scabrous or hirtellous (short, stiff, spreading hairs), usually densely so; plants usually stipitate-glandular distally (on upper stems, array branches, and leaves); leaves and bracts firm, stiffly spreading, sessile.
                       12 Leaf venation conspicuously reticulate, forming isodiametric areoles; leaf margins revolute; plants 5-15dm, arrays typically densely pyramidal with numerous, dense, often subsecund branches; [widespread]
                       12 Leaf areoles elongate and indistinct; leaf margins not revolute; plants 3-9dm, arrays loosely paniculiform; [FL]; [subgenus Virgulus]
                     11 Stems glabrous to pilose or villous (tomentose in S. lanceolatum var. hirsuticaule), leaves and bracts scabrous to glabrous adaxially and glabrous or strigillose, pilose, or villous abaxially (soft or appressed hairs, mostly on veins); plants eglandular; leaves lax.
                          13 Leaf veinlets conspicuously reticulate, forming isodiametric areoles visible on the lower surface; leaves waxy on upper surface (at least when young), the margins usually revolute and entire or weakly toothed; peduncle bracts 5-12 on well-developed peduncles, foliaceous, crowded, closely subtending and often partially obscuring involucres; ray flowers lavender or purple.
                              15 Stem puberulent in lines above; lower leaf surface subglabrous to sparsely scabrous-puberulent; [widespread west of the Appalachians]
                              15 Stem spreading puberulent throughout; lower leaf surface moderately to densely spreading-puberulent; [MO, AR, and LA westward]
                          13 Leaf veinlets indistinct or forming irregular, elongate areoles; leaves not waxy, margins plane or revolute; peduncle bracts, if 5 or more, gradually reduced and grading into phyllaries; ray flowers usually white (except S. simmondsii, S. kralii, and S. hesperium).
                                  17 Leaves thick, firm, margins recurved; involucres (4.5-) 6-8 mm; rays usually pale lavender or lilac; [coastal plain, NC south to FL and AL].
                                    18 Leaves linear, usually none toothed; plants to 8 dm tall; [bogs, wet pine savannas, FL Panhandle and s. AL]
                                    18 Leaves narrowly lanceolate, serrate; plants to 15 dm tall; [wetland and upland habitats, NC to s. FL, west to s. AL]
                                  17 Leaves thin, margins planar or (S. racemosum, S. eulae) recurved; involucres 3-5.6 (-6) mm (-7.2 mm in S. hesperium); rays usually white, sometimes pinkish-tinged (commonly purplish-blue in S. hesperium); [collectively widespread].
                                       19 Disc corolla lobes > 1/2 the length of the corolla limb, recurved; ray laminae (3-) 3.5-5.5 (-8) mm; rays 8-15 (-23).
                                         20 Disc corolla lobes cream (fading purplish), lobes to ¾ length of limb; rays mostly 8-15; plants cespitose; abaxial leaf faces glabrous (midveins ±pilose)
                                         20 Disc corolla lobes usually bright yellow (fading reddish-brown), lobes ca. 1/2 length of limb; rays mostly 16-26 (also keyed below); plants long-rhizomatous; abaxial leaf faces and midveins usually sparsely to densely strigose or strigillose
                                       19 Disc corolla lobes < 1/2 the length of the corolla limb, erect to spreading; ray laminae (4.2-) 5-10 (-14)mm; rays 16-45 (occasionally as few as 12 in S. racemosum and S. tradescantii).
                                           21 Plants short-rhizomatous and cespitose; leaf blades mostly < 1 cm wide, usually held erect-ascending; stems 1.5-6 dm tall, 1-3 mm wide at base; [rocky shores and river shoals, n. NJ northwards].
                                           21 Plants long-rhizomatous and colonial; leaf blades to 3 cm wide, lax or spreading; stems (3-) 6-15 dm tall, 3-6+ mm wide at base; [collectively widespread].
                                             22 Bracts grading into phyllaries, 5-12 on the longer peduncles (1-5 in S. ontarionis, with disc corolla lobes spreading and ca. 1/2 length of corolla limbs); leaf margins often revolute, serrate or less commonly entire; lower stem leaves usually petiolate.
                                               23 Disc corolla lobes mostly widely spreading, about 1/2 length of limbs, usually yellow (fading brownish); ray blades mostly 3.5-5.5 mm; leaves pubescent across face abaxially
                                               23 Disc corolla lobes mostly erect, < 1/2 length limbs, cream-colored or yellow (fading purple or brownish); ray blades > 5 mm; leaves glabrous or (S. racemosum) pilosulous on veins abaxially.
                                                 24 Involucres (4-) 5-6.5 mm; rays mostly (20-) 27-36, blades 8-11 mm; disc corollas yellow (fading brownish); [TX]
                                                 24 Involucres (2.5-) 3.5-4.5 (-5.5) mm; rays mostly (12-)16-20, blades 5-8 mm; disc corollas cream-colored (fading purplish); [widespread].
                                             22 Bracts foliaceous, not grading into phyllaries, 1-3 (-5) (disc corolla lobes < 1/2 length corolla limbs, erect to somewhat spreading); leaf margins flat, entire or with a few remote teeth; stem leaves sessile, slightly decurrent, often not much reduced upward (arrays leafy).
                                                      26 Outer phyllaries 1/3-2/3 the length of the inner ones; heads not usually subtended by large foliaceous bracts.
                                                        27 Stems stout to slender, glabrous or at most hairy in lines at their bases; [collectively widespread].
                                                          28 Heads not congested or congested only distally on lateral branches of arrays; involucres 3.6-5.6 (-6) mm high, and mostly > 4 mm high; [collectively widespread].

Key to Symphyotrichum, Key H: perennial asters with blue-glaucous stems and leaves

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1 Leaves strongly basally disposed, much reduced on the mid and upper stem and the basal and lower stem leaves sometimes withering by anthesis; leaf blades linear or linear-lanceolate (lower) to linear-subulate (upper stem), > 10× as long as wide; leaf margins strongly scabrous; [West Gulf Coastal Plain]
1 Leaves cauline; leaf blades ovate to lanceolate, mostly < 9× as long as wide; leaf margins not strongly scabrous; [widespread].
  2 Larger leaves > 5× as long as wide, rarely > 2.5 cm wide, the bases slightly clasping; [dry glades and barrens]
  2 Larger leaves < 5× as long as wide, often > 2.5 cm wide, the bases strongly clasping; [mesic forests and prairies, widespread northwards]
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