1 Leaves without pustules, but with sparse to dense, resin pits (depressed, circular, pale or translucent pits -- use 10× or more magnification); [collectively widespread].

  2 Heads with (9-) 13-27 ray flowers (count multiple heads); heads with > 20 flowers (disk + ray); larger leaves on a plant 5-12 mm wide; main leaf veins whitish and raised on the lower leaf surface; [collectively south to ne. VA, w. NC, nw. SC, s. TN, and s. IL].

    3 Stems glabrous; leaves glabrous; involucres 4-5 mm high; [mainly Appalachian in our region, from PA south through w. MD, w. VA, e. WV, to w. NC, and nw. SC]

    3 Stems hirtellous to hirsute; leaves hirtellous; involucres 3.6-4.2 mm high; [in our region south to se. VA, sc. VA, sw. NC, s. TN, w. TN, w. KY, and s. IL]

  2 Heads with 5-16 (-19) ray flowers (count multiple heads); heads with < 22 flowers (disk + ray); larger leaves on a plant 1-6 (-7) mm wide; main leaf veins dark and plane (flush) on the lower leaf surface; [collectively widespread].

      4 Leaf midveins glabrous; stems glabrous; leaves 0.5-5 (-7) mm wide.

        5 Axillary shoots usually present in main (midstem) leaf axils

        5 Axillary shoots absent in main (midstem) leaf axils.

          6 Leaves (1.5-) 2-5 (-7) mm wide, the primary midstem leaves mostly > 3 mm wide, 1-3 (- weakly 5)-veined; [s. ON, MI, MN, ND, se. WY south to s. IN, sc. TN, AR, ne. TX, and Panhandle TX]

          6 Leaves 0.5-2 (-5) mm wide, the primary midstem leaves mostly < 2 mm wide, 1-veined; [w. LA, e. TX, and south to se. and s. TX]

      4 Leaf midveins hirsutulous or hirtellous on the lower leaf surface; stems usually sparsely to moderately hirtellous, especially near the nodes and upwards near and in the inflorescence (except glabrous and resinous in E. gymnospermoides); leaves 1-6 (-7) mm wide.

             7 Stems glabrous and resinous

             7 Stems sparsely to moderately hirtellous, especially near the nodes and upwards in and near the inflorescence.

               8 Leaves 1-4 mm wide; axillary shoots present; stems sparsely to moderately hairy on and between the ridges, and from inflorescence to midstem or below; [Atlantic Coastal Plain, s. NJ and se. PA south to ne. NC]

               8 Leaves (2-) 3-5 (-7) mm wide; axillary shoots absent or sometimes present on the upper stem; stems scarious or hirtellous only near the inflorescence and on the stem ridges only; [Atlantic and Gulf Coastal Plain, inland in se. OK].

                 9 Rhizomes densely "hairy" with fibrous roots; [se. OK]

                 9 Rhizomes scaly, not densely "hairy" with fibrous roots; [Coastal Plain, MA and NJ south to s. FL, west to w. LA].

                   10 Leaf surfaces hirtellous (usually across the surfaces as well as on the main veins); [Gulf Coastal Plain, usually in or near tidewater, Panhandle FL west to w. LA]

                   10 Leaf surfaces glabrous, except sometimes hirtellous only on the main veins; [Atlantic Coastal Plain, usually in or near tidewater, from s. NJ (and northwards) south to peninsular FL; Gulf Coast on west side of FL peninsula and FL panhandle west to near the Apalachicola River mouth]