1 Leaves opposite, at least on the lower stem nodes (the leaves higher on the stem sometimes alternate); [tribe Heliantheae or tribe Eupatorieae].

  2 Heads radiate, the rays yellow to orange; disc flowers yellow to orange.

    3 Leaves linear; receptacle epaleate, but densely setose; [extreme s. TX]

      4 Leaves mostly entire, rarely distally 3-lobed, often somewhat glaucous; disc florets 30-100+; receptacle densely setose; pappus of scales

      4 Leaves usually shallowly to deeply 3-9-lobed, green; Disc florets 100+; receptacle with oblong-rectangular paleae; leaves linear or linear-lobed; pappus absent

    3 Leaves lanceolate or broader, 1-5× as long as wide; receptacle paleate; heads borne singly or many; [collectively widespread].

        5 Leaves ovate, rhombic, or pentagonal, unlobed or 3-5-(-7) lobed; leaf blade margins toothed; leaves in part alternate upwards; [of disturbed, suburban areas of FL peninsula]; [tribe Heliantheae; subtribe Helianthinae]

          6 Ray laminae 5-16 mm long; leaf blades 7-33 cm long, the larger deeply 3-7-lobed; petiole bases dilated at base, fused to form a disc of leaf tissue at the stem

          6 Ray laminae 45-70 mm long; leaf blades 2-8 cm long, unlobed or 3-lobed; petiole bases not dilated at base

        5 Leaves lanceolate to oblanceolate, unlobed or obscurely 3-lobed; leaf blade margins toothed or entire; leaves strictly opposite; [tribe Heliantheae; subtribe Ecliptinae].

             7 Leaves obovate to oblanceolate, unlobed, entire; heads (5-) 8-13 (-18+) mm in diameter; cypselas 3-4-smgled, not winged; [of tidally inundated salt and brackish marshes of the outer Coastal Plain, MD to s. FL, west to s. TX]

             7 Leaves lanceolate, sometimes 3-lobed, usually serrate but sometimes nearly entire; heads 4-8 mm in diameter; cypselas flattened and winged; [TX only]

  2 Heads discoid or disciform (ray flowers lacking); disc flowers pink, purple, whitish, yellow, or orange.

               8 Disc flowers yellow to orange

               8 Disc flowers pink, purple, or white.

                 9 Heads small (involucres 2-8 mm high), solitary, axillary in the axils of leaves or leafy bracts (similar to the leaves but smaller) or interpretable as arrayed in bracteate racemes; heads nodding, the involucre 2-7 mm high; [collectively widespread in coastal portions of our area, of maritime situations]; [tribe Heliantheae; subtribe Ambrosiinae]

                 9 Heads small to larger (involucres 3-15+ mm high), many, terminal on the branches of corymbiform or paniculiform arrays; heads erect, the involucre 4-12 mm high; [of Coastal Plain of FL, s. GA, and TX].

                   10 Pappus of 4-10 scales, 0.3-7 mm long; [tribe Heliantheae; subtribe Chaenactidinae]

                   10 Pappus of 5-70 barbellate bristles, 3-12 mm long; [tribe Eupatoriae]

                     11 Leaf blades spatulate to obovate, cuneate to attenuate at the base, rounded or shallowly notched at the apex; leaf margins entire; leaves opposite below, alternate higher on the stems; [native of FL]

                     11 Leaf blades triangular or lanceolate, truncate, cordate, or cuneate at the base, acute to acuminate at the apex; leaf margins serrate; leaves opposite throughout.

                       12 Phyllaries broad, 2-3× as long as wide, the inner phyllaries translucent-scarious white to pinkish at their broadly rounded apices, falling as the head goes to fruit

                       12 Phyllaries narrow, 4-7× as long as wide, the inner phyllaries green at their acute to acuminate apices, persistent on the head in age.

                          13 Involucres 2-3 mm in diameter; phyllaries 7-16 in 1-2 series; disc flowers 3-13 per head; [s. FL only (in our region)]

                          13 Involucres 3-7 mm in diameter; phyllaries 25-35 in 2-3 series; disc flowers 10-60 per head; [TX only (in our region)].

                            14 Disc flowers white (to light pink); [c. TX]

                            14 Disc flowers blue to lavender (rarely white); [extreme s. TX]

1 Leaves strictly alternate.

                              15 Heads radiate (with ray and disc flowers) or pseudoradiate (with pseudoradiate flowers only.

                                16 Rays white, pink, or rose.

                                  17 Rays pink or rose, 30-50 (-70); sprawling viny shrub to 40 dm tall; leaves ovate, averaging ca. 3× as long as wide, with clasping base, with a midvein and lateral veins and tertiary reticulation

                                  17 Rays white, 5-34+; shrubs 2-30 dm tall; leaves either obovate to oblanceolate, averaging ca. 4× as long as wide, dentate, or linear, ca. 10× as long as wide, entire, cuneate.

                                    18 Rays white, 5-11 (-15); leaves linear, ca. 10× as long as wide, entire; [native, s. and se. TX]

                                    18 Rays white, 21-34+; leaves obovate to oblanceolate, averaging ca. 4× as long as wide, dentate; [non-native, known in our region only from NY]

                                16 Rays or pseudorays yellow, orange-yellow, or light creamy yellow.

                                       19 Heads pseudoradiate, with 11-25 pseudoray flowers and 0 disc flowers; leaves 8-70 mm wide

                                       19 Heads radiate, with (0-) 1-11 (-15) ray flowers and 1-15 (-20) disc flowers; leaves (or their segments) 0.5-10 mm wide.

                                         20 Phyllaries in 1-2 series and equal or subequal in length to one another, the phyllaries often coherent/fused (the involucre thus appearing as a cylinder with ribs extending from base to top; calyculus (of bracts subtending the phyllaries and differing from them in texture, color, or orientation) present; [tribe Senecioneae]

                                         20 Phyllaries in 3-17 series and unequal in length (imbricated); calyculus absent.

                                           21 Rays light creamy yellow, 5-11 (-15); involucre 3-5 (-7) mm in diameter

                                           21 Rays bright yellow, (0-) 1-9; involucre 1-2.5 (-3) mm in diameter.

                                             22 Pappus of 40-60 barbellate bristles; ray blades 4-6 mm long; leaf surfaces minutely pebbled; intricately branched shrubs to 1 m tall, with persistent sterile shoots with evergreen leaves and annual flowering shoots (the entire shoot and leaves deciduous); [Coastal Plain, se. NC south to Panhandle FL and s. MS]

                                             22 Pappus absent, a low coroniform structure, or of scales; ray blades 2-3.5 mm long; leaf surfaces planar/revolute; shrubs 1-15 dm tall, not differentiated into evergreen, sterile shoots bearing deciduous, fertile shoots; [OK and TX westwards, very rarely as a waif eastwards].

                                               23 Pappus of 5-10 elongate scales

                                               23 Pappus absent or a low (< 0.1 mm high) crown

                              15 Heads discoid (with disc flowers only).

                                                 24 Pappus absent; leaves 1-2× pinnately or 1× palmately lobed.

                                                    25 Leaves 1-pinnately lobed, the many (>21) lobes mostly < 1.5 mm long and wide

                                                 24 Pappus of bristles; leaves unlobed (the margins entire or serrate).

                                                      26 Plants dioecious, either male or female; heads either staminate, with 10-50 flowers, or pistillate, with 20-150 flowers

                                                      26 Plants hermaphroditic; heads bisexual, with 5-25 flowers, either all perfect (bisexual), or a mixture of perfect (bisexual) and functionally staminate flowers.

                                                        27 Leaves strongly basally disposed, crowded in the lowermost, woody or semiwoody portion of the stem

                                                        27 Leaves on the stem.

                                                          28 Leaves lanceolate to ovate (broadest below the midpoint); leaf margins entire to coarsely toothed.

                                                            29 Heads in leafy, paniculate arrays; leaf blades coarsely dentate, 0.5-4 cm long; shrubs to 12 dm tall; [c. and e. TX]

                                                            29 Heads borne in leafless, corymbiform arrays; leaf blades entire to denticulate, 5-16 (-20) cm long; shrubs to 40 dm tall; [FL and s. TX]

                                                          28 Leaves obovate, spatulate, or orbiculate (with rounded apex) or elliptic (with acute to acuminate apex), broadest at or beyond the midpoint; leaf margins entire.

                                                              30 Leaf blades obovate, spatulate, or orbiculate, rounded or slightly notched at the apex; leaf blade surfaces gray-green on both surfaces, granular when young; disc flowers 5 per head; [FL]

                                                              30 Leaf blades elliptic, acute to acuminate at the apex; leaf blade strongly bicolored above and below, the upper surface dark green and glabrate, the lower surface densely and finely tomentose and strongly whitened, the upper surface dark green and glabrate or glabrous; disc flowers 4-25 per head; [s. TX]

1 Receptacle paleate (bearing receptacular bracts which individually subtend at least some of the flowers of the head).

  2 Involucres absent or vestigial, usually with 0 phyllaries; heads very small, < 6 mm high, < 4 mm wide; annuals, < 4 dm tall; disc corollas hidden or dingy in color; [tribe Gnaphalieae]

    3 Bisexual flowers (1-) 2-10 (-11), pappus of (11-) 13-28+ bristles visible in heads; functionally staminate flowers 0.

      4 Receptacles cylindric to clavate (5-15× as tall as the diameter); most pistillate paleae open to ± folded (at most each enfolding, not enclosing a floret; apices acuminate to aristate); innermost paleae erect to ascending in fruit; cypselae mono- morphic (the outer ± equaling the inner)

      4 Receptacles fungiform to obovoid (0.4-1.6× as tall as the diameter); most pistillate paleae ± saccate, each ± enclosing a floret, apices blunt; innermost paleae spreading in fruit; cypselae dimorphic (the outer longer than the inner)

    3 Bisexual flowers 0 or 2-7, pappi 0; functionally staminate flowers 0 or 2-5, pappi 0 or of 1-10 (-13) bristles hidden in heads

        5 Paleae of the bisexual or staminate flowers flat to concave, not enclosing florets, apices entire; cypselae glabrous; [mainly west of the Mississippi River, rarely east (as in MS, AL, GA, and SC]

        5 Paleae of the bisexual flowers saccate, each enclosing a floret, apices 2-fid or 3-fid; cypselae (at least the outer) strigose; [se. Texas]

  2 Involucres present, conspicuous, of many phyllaries; heads larger, 2-20+ mm wide; perennials or coarse annuals, 2-25 dm tall; disc corollas apparent, yellow, white, or pink to purplish.

          6 Disc flowers yellow or greenish yellow; [either native of s. TX southwards, or a waif]

             7 Phyllary margins and tips scarious; fresh foliage aromatic

             7 Phyllary margins and tips herbaceous; fresh foliage not aromatic

          6 Disc flowers white or whitish to pink or purple; [collectively widespread].

               8 Heads in corymbiform arrays; heads bisexual; involucres not burlike or nutlike, lacking tubercles or hooked or straight prickles or spines; leaves lanceolate, unlobed, cuneate at base

                 9 Heads lacking ray flowers; disc flowers pink (rarely nearly white); [Coastal Plain; FL and GA]

                 9 Heads with 5 white (fading to cream), scoop-shaped, inconspicuous ray flowers (keyed here as a 'failsafe'); disc flowers white; [widespread in our region]

               8 Heads in spiciform or racemiform arrays; heads unisexual (each head either with only female or only male flowers); involucres burlike, with tubercles or straight or hooked spines or prickles; leaves ovate or broader (in outline), often pinnatifid or bipinnatifid, truncate, cordate, or cuneate at base; [collectively widespread in our region].

                   10 Involucres of pistillate heads (burs) 1-4 mm long, with (1-) 5-12+ straight spines; larger leaves bipinnatifid

                   10 Involucres of pistillate heads (burs) 10-40 mm long, with 30-75+ hooked prickles; phyllaries larger leaves pinnatifid or unlobed

1 Receptacle epaleate (lacking receptacular bracts individually subtending flowers, but the receptacle sometimes bearing bristles, setae, hairs, or pits with laciniate margins.

                     11 Flowers white, pink, purple, or bluish.

                       12 Annuals, (1-) 2-10 (-30+) cm tall; corollas whitish, inconspicuous, absent on most of the (pistillate) flowers; leaves 2-3× pinnati-palmately lobed into linear segments; cypselae with an apical spine

                       12 Perennials, 10-150 cm tall; corollas at least light pink and often darker pink, purple, or blue, conspicuous, present on all flowers; leaves pinnately lobed or entire, the segments not linear; cypselae not spined.

                          13 Heads ovoid, 10-21 mm long; flowers 15-40 mm long, with long, narrow lobes; phyllaries >30, in 6+ series, and the apices often with a fringe of appendages and/or a spine tip; basal and lower stem leaves usually pinnately lobed (to entire and unlobed); [widespread in our region, especially northwards]

                          13 Heads cylindrical, 2-6 mm long; flowers ca. 3 mm long, with deltate lobes; phyllaries 12-15 in 2-3 series, herbaceous and unadorned; basal and lower stem leaves entire and unlobed; [Coastal Plain of FL and GA]

                     11 Flowers yellow, cream, or rarely red-tinged.

                            14 Leaf blades unlobed.

                              15 Heads 3-4 (-6) mm in diameter, solitary; plants 0.3-3 dm tall; [ballast waif, especially in wet, saline places]

                              15 Heads (3-) 5-20+ mm in diameter, solitary or borne in corymbiform or paniculiform arrays; plants 1.5-15 dm tall.

                                16 Involucres 8-20+ mm in diameter; cypselae 1.5-4.5 mm long

                                16 Involucres (3-) 5-8 (-10) mm in diameter; cypselae 1.5-2 mm long

                            14 Leaf blades 1-3× pinnately or palmately lobed into linear or spatulate segments.

                                  17 Annual 0.1-5 dm tall.

                                    18 Disc corollas cream to pale yellow, 0.5-0.8 mm long; fresh plants malodorous; [waif]

                                    18 Disc corollas greenish yellow, 1.1-1.3 mm long; fresh plants pineapple-scented; [common weed, especially northwards in our region]

                                  17 Perennial, biennial or annual 4-15 dm tall.

                                       19 Heads borne in corymbiform arrays; flowers 60-300+ per head