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Key to Symphyotrichum, Key A: perennial asters with petiolate, cordate-bladed lower leaves [of subgenus Symphyotrichum, sections Heterophylli and Concinni]
1 Disc flowers (8-) 10-25 (-30); ray flowers 8-20 (-25); involucre 3.8-7 mm high (or to 8 mm high in S. oolentangiense); phyllary tips appressed (or the outer phyllaries loose or spreading).
....3 Cauline leaf blades sessile and cordate-clasping, or petiolate, the petiole strongly dilated to a cordate-clasping base, or both
........5 Basal leaves shallowly cordate to truncate; phyllaries with short diamond shaped blaze (1-1.5× as long as wide) or linear-lanceolate-shaped blaze (> 4× as long as wide), green.
..........6 Phyllaries with linear-lanceolate-shaped green blaze (> 4× as long as wide)
......4 Lower stems glabrous to sparsely hirsute; upper stems densely hirtellous to hirsute; [mainly west of the Appalachians].
............ ..8 Phyllaries with short diamond-shaped green blaze (1-1.5× as long as wide); basal and lower stem leaves mostly crenate to entire; upper stem leaves entire.
............ ....9 Plants with only the basal and lower stem leaf blades cordate or subcordate, the midstem and upper leaves not petiolate and with cuneate bases; phyllary faces glabrous; disc flowers (15-) 20-25 (-30)
............ ..8 Phyllaries with elongate green blaze (> 2× as long as wide); basal and lower stem leaves serrate or crenate; upper stem leaves serrate or crenate (to entire).