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Keyed in multiple places:

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Key to Asteraceae, Key M: Herbaceous composites with the leaves alternate or basal and the heads radiate, the rays white, pink, purple, and with a pappus of bristles only

Asteraceae

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1 Head 1 per plant (individual rosette); stems 0.1-0.3 dm tall; [TX and OK westwards]
1 Heads 5-300+ per (well-developed) plant; stems 0.3-35 dm tall; [collectively widespread].
  2 Stems with numerous thorns (1-2 cm long, modified axillary branches), and few or no leaves
  2 Stems leafy, not armed with thorns.
    3 Leaves unlobed; plant perennial from caudices, crowns, or rhizomes.
      4 Annuals from taproots; ray florets 0.3-7 mm long.
        5 Ray laminae 0.3-1.0 mm long; cypselas 1.0-1.5 mm long, compressed, 1-nerved on each face
        5 Ray laminae 1.3-7 mm long; cypselas (1.2-) 1.5-2.7 (-3) mm long, compressed or not, 5-18-nerved.
          6 Disc flowers 25-35 per head; ray flowers in 1 series
      4 Perennials from caudices, crowns, or rhizomes; ray florets > 3 mm long.
             7 Basal and lower stem leaves petiolate, with blades cordate to rounded at the base
               8 Heads borne in corymbiform arrays, the branches often subtended by large and leaf-like bracts; phyllaries < 2.5 (-3)× as long as wide, often > 1 mm wide; plants (in most species) colonial by rhizomes; rays (in most species) white; phyllaries (in many species) glandular
               8 Heads borne in paniculiform arrays, the branches bearing small and narrow bracts; phyllaries > 3× as long as wide, often < 1 mm wide; plants (in most species) solitary; rays (in most species) blue, violet, or pink; phyllaries eglandular
             7 Basal and lower stem leaves sessile (sometimes cordate-clasping), or if petiolate then with cuneate to attenuate bases.
                 9 Rays pink, purple, lavender, blue, or pale pink [plants with pale pink rays may need to be keyed both ways].
                   10 Heads borne either in flat-topped or rounded, corymbose arrays, or in narrow racemiform or spiciform panicles, or solitary.
                     11 Leaves 1.2-4.0 cm long, 1-4 mm wide, stiff, scabrous margined and weakly spine-tipped; plants 1-7 dm tall; pappus in 2 series, the inner much longer than the outer (ca. 1 mm long) bristles
                     11 Leaves either longer or broader or both, herbaceous; Leaves (5-) 13-45 mm wide, herbaceous, neither scabrous-margined nor spine-tipped; plants 4-30 dm tall; pappus not divided into distinct inner and outer series.
                       12 Plants 10-35 dm tall; larger leaves (basal or low on the stem) with cuneate or attenuate bases, the blades 30-50 cm long; [non-native, rarely persistent or spreading from horticultural use]
                       12 Plants 1-12 dm tall; larger leaves with blades 2-20 cm long; [natives, collectively widespread and common in our region]
                 9 Rays white (or very slightly pink-flushed).
                          13 Heads borne either in flat-topped or rounded, corymbose arrays, or in narrow racemiform/spiciform panicles, or solitary.
                                16 Disc flowers yellow (and often fading to pink or purplish).
                                  17 Rays 2-7, the ray ligules 2-11 mm long, often twisted or contorted; phyllaries whitish with a distinct green tip, the green area about as wide as long
                                  17 Rays (8-) 9-40, the ray ligules 4-20 mm long, generally planar (or neatly coiling at post-maturity); phyllaries various.
                                    18 Pappus not divided into distinctively different outer and inner series; leaves toothed or entire.
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Key to Solidago, Key O: Key to "erect goldenrods" -- with basally disposed leaves and elongate, cylindrical inflorescences (subgenus Solidago, section Erectae]

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1 Phyllaries very narrow, ca. 0.5 (-0.75) mm wide, linear-lanceolate, very gradually tapering to a pointed or minutely rounded tip; [subgenus Solidago, section Erectae, series Puberulae].
  2 Stems glabrous proximally up to mid-stem; rays mostly 6-9; inner phyllaries usually striate with 2 prominent secondary veins
  2 Stems finely hairy throughout with minute strigillose hairs; rays mostly 9-16; inner phyllaries not striate.
    3 Leaves 20-50 (-60) per stem; midstem leaves usually 4-5 cm long; phyllaries attenuate; [Mountains and Piedmont of GA northward, and Coastal Plain from VA northward]
    3 Leaves (20-) 50-120 per stem; midstem leaves usually 1-4 cm long; phyllaries acute to acuminate; [Coastal Plain from DE southward]
1 Phyllaries broader, (0.75-) 1.0-1.5 mm wide at mid-length, ovate to lanceolate, acute to obtuse or broadly rounded; [subgenus Solidago, section Erectae, series Erectae].
(c) Ware, Richard & Teresa - CC-BY-NC, permission granted to NCBG
      4 Rays yellow (may turn pale yellow with age).
        5 Involucres (6-) avg. 7.2 (-9.5) mm high
        5 Involucres 3.5-6.5 mm high.
          6 Leaves and stems sparsely to densely hairy with long, spreading (to less typically appressed) hairs
          6 Leaves and upper stems glabrous or nearly so, the lower stems often somewhat hairy with short hairs (often feeling slightly scabrous).
(c) Ware, Richard & Teresa - CC-BY-NC, permission granted to NCBG
             7 Inflorescence thyrsiform, very slender, usually linear in outline but sometimes with a few widely spaced elongate branches; cypsela bodies 2.2-3.0 mm long; ray flowers often pale yellow; [MA to se. IN, south to GA and MS, mostly avoiding the Coastal Plain southward]
(c) Fleming, Gary P.
(c) Pogacnik, Shaun - CC-BY-NC, permission granted to NCBG
             7 Inflorescence panicle-like, usually with several to many ascending branches and ovoid in outline; cypsela bodies 1.1-2.0 mm long; ray florets golden yellow; [MA to GA, west to SD and scattered south from CO to ne. NM].
(c) Graeff, Alex - CC-BY-NC-ND, permission granted to NCBG
               8 Mid-stem leaves 0.4-1.5 (-2.0) cm wide; basal leaves 0.8-2.0 cm wide, entire or slightly serrate, present or absent at flowering
(c) Faulkner, Erin - CC-BY-NC, permission granted to NCBG
               8 Mid-stem leaves usually > 2 cm wide; basal leaves (2.0-) 3.0-5.5 cm wide, coarsely serrate, present at flowering