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Key to Erigeron

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1 Ray flowers 0.2-1 mm long; plants annual from a taproot.
1 Ray flowers 3-10 mm long; plants annual, biennial, or perennial.

Key to Erigeron, Key A: Key to "conyzoid" Erigeron

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1 Plants diffusely branched from the base and throughout; plants 1-2.5 (-3) dm tall
1 Plants with a well-developed central axis, sparingly branched (unless on coastal dunes, mowed, or otherwise injured); plants 1-15 dm tall.
  2 Involucre 4-6 mm high, densely pubescent; pistillate flowers 20-150 (or more) per head.
    3 Cauline leaves characteristically linear to linear-oblanceolate; capitulescence corymbiform to racemiform, less commonly thyrsoid; fruiting receptacles (2-) 2.5-4 (-5) mm wide, not alveolate or sometimes the inner florets barely so; phyllaries linear-lanceolate, relatively thick and opaque, 0.3-0.5 mm wide, green to greenish brown with a narrow, orange-resinous midvein, hispid-hirsute with thick-based hairs, sometimes purple-tipped, inserted on a ring of fused tissue; pistillate florets ca. 40-150, in (2-) 3-6 series
    3 Cauline leaves characteristically narrowly lanceolate-elliptic to lanceolate or oblanceolate; capitulescence usually paniculate-thyrsoid; fruiting receptacles 1.5-2.5 mm wide, weakly but distinctly alveolate (lens), outer to inner florets; phyllaries narrowly ovate, relatively thin and translucent, 0.5-0.8 mm wide, central part yellow-brown with an inconspicuous midvein, loosely strigose with thin-based hairs, never purple-tipped, inserted at apex of peduncle; pistillate florets ca. 20-50, in 2-3 series
  2 Involucre 3-4 mm high, glabrous or very sparsely pubescent; pistillate flowers mostly 25-45 per head.
      4 Stem coarsely spreading-hirsute; leaves ciliate, the larger generally with a few to many coarse teeth; phyllaries green-tipped or white-tipped
      4 Stem glabrous or with widely scattered, appressed hairs; leaves with a few cilia toward the base, generally entire; phyllaries purple-tipped

Key to Erigeron, Key B: Key to "erigeronoid" Erigeron

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1 Stem leaves sessile; pappus of the pistillate (ray) flowers consisting only of a few short, slender scales, < 1 mm long (visible at 20× magnification); annual or perennial (rarely biennial); [section Phalacroloma].
  2 Stem leaves many, mostly toothed, the larger > 1 cm wide; pubescence of the mid-stem long and spreading, of dense, flattened hairs; plants to 15 dm tall.
  2 Stem leaves few, mostly entire, the larger usually < 1 cm wide; pubescence of the mid-stem usually short and appressed, of flattened hairs, mainly restricted to the lower stem (or entirely absent); plants to 8 dm tall.
    3 Plants perennial, rhizomatous; [plants of shallow soil over calcareous rock].
      4 Basal leaves oblanceolate to narrowly obovate or spatulate, (3.2-) 3.8-15 (-21) mm wide; cauline leaves glabrous, except along the midvein and the ciliate margins; [of limestone glades and barrens of c. TN, nw. GA, and n. AL]
      4 Basal leaves linear-oblanceolate, 1-3.5 (-6) mm wide; cauline leaves sparsely to moderately strigillose; [of dolostone glades of c. AL (Bibb Co.)]
    3 Plants annual (rarely biennial), lacking rhizomes; [of various, often weedy, habitats]
        5 Plants lacking flattened trichomes throughout (absent on the stems and the phyllaries]; plants sexual, diploid, with well-formed pollen grains < 15 µm in diameter; [of w. LA and e. TX]
        5 Plants often with flattened trichomes on the stems; plants asexual, apomictic, with very variable, poorly formed pollen grains, some > 17 µm in diameter; [widespread]
          6 Phyllary hairs flattened, 0.5-1.2 mm long; stem hairs appressed to spreading, 0.5-1.0 mm long
          6 Phyllary hairs terete, mostly 0.1-0.5 mm long; stem hairs appressed to spreading, 0.1-0.4 (-0.8) mm long
1 Stem leaves relatively large and clasping, or small and sessile (in E. vernus); pappus of the pistillate (ray) flowers of elongate capillary bristles (sometimes also with scales); plants biennial or perennial.
             7 Plants trailing or ascending, rooting at the nodes, and with stolons; [section Cincinnactis]
             7 Plants erect (sometimes the shoots curved at the base but ultimately vertical).
               8 Stem leaves not clasping; basal leaves fleshy; rays 25-40, white, 0.5-1.3 mm wide; [of moist to wet habitats of the Coastal Plain]; [section Erigeridium]
               8 Stem leaves clasping; basal leaves herbaceous; rays 50-400, pink, blue, purplish, or white, either 0.3-0.5 mm wide (in E. philadelphicus var. philadelphicus, E. quercifolius, and E. tenuis) or 0.8-1.2 mm wide (in E. pulchellus var. pulchellus); [of more general distribution and habitat].
                 9 Disk corollas 4-6 mm long; rays 50-100, 0.8-1.2 mm wide; plants clonal by rhizomes and stolons; [section Pauciflori].
                   10 Stems and leaves glabrous
                   10 Stems and leaves densely pubescent with long hairs
                 9 Disk corollas 2.0-3.2 mm long; rays 60-400, 0.3-0.5 mm wide; plants solitary from a caudex.
                     11 Involucre 4-6 mm high; rays 150-400, white to deep pink, 5-10 mm long; [section Quercifolium]
                     11 Involucre 2.5-4 mm high; rays 60-250, blue-lavender (rarely white to pink), 2.5-5 (-6) mm long.
                       12 Pappus simple; stem spreading pubescent throughout (or appressed pubescent in the upper third only); rays 100-250; [section Quercifolium]
                       12 Pappus double, with short outer setae in addition to the long slender bristles; stem appressed pubescent in at least the upper half; rays 60-120; [section Phalacroloma]