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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 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
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