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| 1 Disc corolla lobes ½ - ¾ of the length of the corolla limb (the flared portion above the narrow corolla tube); disc corolla lobes spreading to reflexed. |
| ..2 Plants cespitose, with short, branched caudices or short-rhizomatous; abaxial leaf faces glabrous, midveins ± densely pilose (rarely glabrate); ray flowers 8-15 (-23); disc corollas white to cream turning pink to purplish, lobes strongly reflexed (lengths 1/2-3/4 corollas); [wide variety of habitats] |
| ..2 Plants colonial, long-rhizomatous; abaxial leaf faces and midveins usually sparsely to densely strigose or strigillose, sometimes glabrous (var. glabratum); ray flowers (10-) 15-26; disc corollas cream to light yellow turning purple to brown, lobes spreading (lengths ca. 1/2 corollas); [bottomlands and other wetlands] |
| 1 Disc corolla lobes < ½ the length of the corolla limb (the flared portion above the narrow corolla tube); disc corolla lobes usually erect. |
| ....3 Peduncles long (at least some > 2 cm long), with numerous small, closely-spaced bracts mostly 1-4 mm long and much smaller than the leaves; plants mostly not strongly rhizomatous (sometimes with multiple stems from short-creeping rhizomes); plants mostly < 10 dm tall. |
| ......4 Involucres 7-12 mm high; rays light blue to purple; mid-stem leaves without axillary fascicles; [C. and s. IL and MO south to AR and e. OK] |
| ......4 Involucres (3-) 4.5-6.3 mm high; rays pale blue, pink, lavender, or white; mid-stem leaves usually with axillary fascicles; [collectively widespread] |
........5 Peduncle bracts, at least lower and middle, mostly spreading or reflexed, oblong to linear-oblong, obtuse to subacute (rarely abruptly mucronate) |
| ........5 Peduncle bracts mostly ascending (-appressed), sometimes spreading, oblong-linear to linear-subulate, acute. |
| ..........6 Cauline leaves 3-7 cm long; branches few; peduncles long; rays 14-17 (-20) |
| ..........6 Cauline leaves to 15 cm long; branches abundant; peduncles long, short, or absent; rays 13-25. |
| ............ 7 Stems glabrate; branches not crowded; most peduncles long, their bracts short and of ± uniform length and shape |
| ............ 7 Stems glabrate, puberulent, or strigose; branches crowded; most peduncles short to absent, their bracts not uniform, some long and narrow. |
| ............ ..8 Stems sparsely and finely puberulent; inflorescence small and terminal; rays 13-16 (-20) |
| ............ ..8 Stems glabrate, scabrous-puberulent, or strigose with coarse hairs; inflorescence diffuse; rays 20-25 |
| ....3 Peduncles short (mostly < 2 cm long), sparsely bracteate or with leaves rather than bracts in close proximity to the heads; plants strongly colonial from creeping rhizomes; plants mostly > 10 dm tall; |
| ............ ....9 Involucres (2.5-) 3.5-4.5 (-5.5) mm high; rays mostly < 20, usually white (rarely pink); ray blades 3-8 mm long; plants 3-9 (-10) dm tall. |
| ............ ......10 Heads densely crowded in spikelike racemes, the peduncles mostly < 7 mm long |
| ............ ......10 Heads in loose racemes or scattered on branch ends, the peduncles mostly 10-20 mm long |
| ............ ....9 Involucres 3-7 (-8) mm high; rays mostly > 16, white, pink, or violet; ray blades mostly 6-15 mm long; plants 3-15 (-20) dm tall. |
| ............ ........11 Leaves thin, planar; peduncle bracts 1-3 (-5). |
| ............ ..........12 Outer phyllaries > 2/3 the length of the inner ones; heads usually subtended by large foliaceous bracts |
| ............ ..........12 Outer phyllaries 1/3-2/3 the length of the inner ones; heads not usually subtended by large foliaceous bracts. |
| ............ ............ 13 Plants 1.5-6 dm tall; [n. NJ northwards] |
| ............ ............ 13 Plants mostly 6-15 dm tall; [collectively widespread] |
| ............ ............ ..14 Stems stout, moderately to densely short-woolly or tomentose from their bases upward; [s. IL northwards] |
| ............ ............ ..14 Stems stout to slender, glabrous or at most hairy in lines at their bases; [collectively widespread]. |
| ............ ............ ....15 Heads congested on lateral branches of arrays; involucres 3-4 mm high; [PA, s. OH, n. KY, and AR northwards] |
| ............ ............ ....15 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]. |
| ............ ............ ......16 Leaves linear to oblanceolate, reduced in arrays; involucres 3.6-5 (-6) mm high; rays white to purplish |
| ............ ............ ......16 Leaves broadly oblanceolate, not much reduced in arrays; involucres usually 4-5.6 mm; rays white |
| ............ ........11 Leaves stiff, margins revolute; peduncle bracts 5-12 or more (except 1-3 in S. boreale). |
| ............ ............ ........17 Ray blades (7) 10-15 (20) mm long, white or pale rose to lavender; peduncle bracts 1-3 |
| ............ ............ ........17 Ray blades 5-11 (-12) mm long, pale lilac to medium blue or medium purple; peduncle bracts 5-12 or more. |
| ............ ............ ..........18 Leaf veinlets obscure, or if more conspicuous then the areoles obviously longer than broad. |
| ............ ............ ............ 19 Leaves linear, usually none toothed; plants to 8 dm tall; [bogs, wet pine savannas, FL Panhandle and s. AL] |
| ............ ............ ............ 19 Leaves narrowly lanceolate, serrate; plants to 15 dm tall; [wetland and upland habitats, NC to s. FL, west to s. AL] |
| ............ ............ ..........18 Leaf veinlets conspicuously reticulate on the lower surface, the areoles nearly isodiametric. |
| ............ ............ ............ ..20 Leaves thin, linear to linear-lanceolate |
| ............ ............ ............ ..20 Leaves rather thick, lanceolate to elliptic. |
| ............ ............ ............ ....21 Leaves harshly scabrous above |
| ............ ............ ............ ....21 Leaves glabrous or nearly so above. |
| ............ ............ ............ ......22 Stem spreading puberulent throughout; lower leaf surface moderately to densely spreading-puberulent; [MO, AR, and LA westward] |
| ............ ............ ............ ......22 Stem puberulent in lines above; lower leaf surface subglabrous to sparsely scabrous-puberulent; [widespread west of the Appalachians] |