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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]
............ ....9 Free tips of phyllaries tightly involute, long-acuminate; stem leaves not crowded, often broader, not upcurved; [subgenus Symphyotrichum]
............ ..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]
............ ......10 Stems pubescent in lines distally (densely hirsute in S. puniceum), plants eglandular; leaves usually toothed, lower winged-petiolate, upper auriculate-clasping or cuneate; [subgenus Symphyotrichum]
............ 7 Phyllary tips appressed to ascending, faces glabrous (rarely sparsely strigillose).
............ ........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
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