1 Pappus present, of 5-60 barbellate bristles; receptacle naked (without paleae or well-developed bristles); [tribe Heliantheae; subtribe Eupatoriae].

  2 Plant a twining herb, phyllaries and disk florets 4 per head

  2 Plant stiffly erect to sprawling but never twining, phyllaries and disk florets usually > 4 per head.

    3 Leaves in whorls of 3-7, > 2 cm wide

    3 Leaves opposite, rarely alternate or whorled, if whorled, < 2 cm wide.

      4 Cypselae rostrate (with long beaks); the achene portion not bearing ribs

      4 Cypselae not beaked, the achene variously ribbed.

        5 Achenes (and ovaries) (3-) 4-5-ribbed; outer phyllaries not noticeably longitudinally striate.

          6 Heads pink to blue.

             7 Phyllaries in 4-6+ series, deciduous

             7 Phyllaries in 2-4 series, persistent (or deciduous in Praxelis).

               8 Heads pink (rarely bluish); receptacles flat; florets 18-25 per head; leaves sometimes gland-dotted

               8 Heads blue; receptacles conic; florets 25-70 per head; leaves gland-dotted.

                 9 Bristles ca. 30; florets 35-70+; phyllaries ca. 25, subequal, persistent

                 9 Bristles ca. 40; florets 25-30; phyllaries 15-25, unequal, deciduous (absence apparent in fruit)

          6 Heads white to cream or, rarely, pale lilac.

                   10 Florets 3-7 per head

                   10 Florets at least 9 per head.

                     11 Phyllaries not strongly imbricate, with the principal ones subequal and sub-biseriate; petioles 0.5-10 cm

                     11 Phyllaries clearly imbricate, in 3+ series, the margins usually glandular; some species epetiolate

1 Pappus either absent, or of scales, setae, or awns; receptacle naked, paleate, or bearing bristles.

                       12 Leaves whorled, linear, < 2 mm wide; head solitary; [aquatic herb growing in shallow stagnant water]

                       12 Leaves opposite (or alternate in part), broader in shape and > 5 mm wide; heads typically not solitary; [terrestrial or wetland plants].

                          13 Receptacles naked (epaleate).

                            14 Pappus of 2-12 scales; heads white, pink, or blue (yellow in Schkuhria).

                              15 Heads with 20-125 florets; leaves serrate or ± dentate (at least distally); [rarely naturalized exotics or s. TX/FL natives]; [tribe Eupatorieae].

                                16 Leaves petiolate; corolla tube glabrous, typically blue or lavender colored (sometimes white tinged); heads with 20-125 florets; [naturalized exotics or s. FL native]

                                16 Leaves sessile; corolla tube glandular-pubescent, typically white colored (sometimes pink-purple tinged); heads with 75-125 florets; [s. TX native]

                              15 Heads with 10-30 florets (or fewer in Schkuhria); leaves entire; [natives, of FL, s. GA, MS, and TX in our area]; [tribe Heliantheae; subtribe Chaenactidinae].

                                  17 Leaves 3-5 lobed (or foliolate); cypselae with curled hairs (Florestina tripteris) or villous on angles (Schkuhria pinnata); [s. TX in our area or ne. waif].

                                    18 Heads discoid, corolla white; cypselae with curled hairs; [s. TX in our area]

                                    18 Heads discoid, sometimes with 1 (-2) diminuitive rays, corolla (of discs) yellow; cypselae villous, at least at bases or on angles; [waif of ne US, native in sw. US]

                                  17 Leaves simple or unlobed; cypselae with straight hairs; [variously distributed in s. GA and FL w. to MO and s. TX]

                            14 Pappus none, or of a few bristles or irregular coroniform lobes; heads green to yellow.

                                       19 Heads bright yellow, closely aggregated into corymbiform arrays of flat-topped to dome-shaped glomerules

                                       19 Heads greenish or greenish yellow, borne in spiciform, racemiform, or paniculiform arrays.

                                         20 Heads in paniculiform arrays, all or most of the heads not subtended by bracts

                                         20 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract

                          13 Receptacles with paleae or well-developed bristles (the pales sometimes modified into specialized perigynia or burs surrounding the achene).

                                           21 Involucre of four decussate, deltoid bracts (the outer two large and longer than and often enclosing the flowering heads); pappus absent; paleae tightly enclosing the cypselae; plants rooting at the nodes, sometimes free-floating in water; [uncommon non-native, c. FL]

                                           21 Involucre not of four decussate, deltoid bracts; plants not with the above combination of characters; [widespread natives and non-natives]

                                             22 Heads small, less than 1 cm in diameter at anthesis (the female heads enlarging in Xanthium); disc florets dull white or suffused with green or purple; florets mainly unisexual (either in the same heads and then males central and females peripheral, or in separate female and male heads); female florets 0-8 per head; [tribe Heliantheae; subtribe Ambrosiinae].

                                               23 Heads unisexual; cypselas shed within an indurated bur or “nut” with hooked or straight spines developed from the phyllaries and/or paleae.

                                                 24 Involucre of the female heads with tubercles or straight spines developing from the phyllaries; burs 1-8 mm long

                                                 24 Involucre of the female heads with hooked spines developing from the phyllaries/paleae; burs 10-35 mm long

                                               23 Heads bisexual, with functionally male and female flowers in the same head; cypselas shed individually, not enclosed.

                                                    25 Heads in paniculiform arrays, all or most of the heads not subtended by bracts

                                                    25 Heads in spiciform or racemiform arrays, each 1 (-2) heads subtended by a bract

                                             22 Heads larger, mostly > 1 cm in diameter at anthesis; disc florets conspicuously white, yellow, pale yellow, or purple; florets mainly bisexual; female florets > 12 per head (except 2-8 in Polymnia and 8-15 in Verbesina occidentalis).

                                                      26 Leaves strongly basally disposed, the basal-most leaves sitting almost flat on the ground and overlapping; disc flowers maroon-purple

                                                      26 Leaves mainly or strictly cauline (not basally disposed); disc flowers white, yellow, or reddish-brown.

                                                        27 Disc flowers bright yellow or reddish-brown.

                                                          28 Involucre of phyllaries subtended by a calyculus of bracts obviously different in color, texture, and shape than the phyllaries.

                                                            29 Phyllaries usually distinct, rarely connate proximally; disk florets bright yellow

                                                            29 Phyllaries connate (both proximally-distally connate); disk florets yellow to reddish-brown

                                                          28 Involucre of phyllaries not subtended by a calyculus (phyllaries sometimes in 2+ series, but without obvious calyculi below).

                                                              30 Plants erect; heads without ray florets; [wet pine savannas and bogs; FL panhandle]

                                                              30 Plants primarily prostrate or trailing, sometimes erect; heads with or without ray florets; [habitats various, widespread natives and non-natives]

                                                        27 Disc flowers bright white or pale yellow.

                                                                 31 Stems not winged; plants erect or spreading.

                                                                   32 Cypselae 3-4 angled; pappus falling (of 2-12 awns or bristles); leaf margins irregularly crenate to serrate, the surfaces sometimes roughened but lacking glands; [e. of TX]

                                                                   32 Cypselae 5-ribbed; pappus absent; leaf margins entire or serrulate, the surfaces gland-dotted; [s. TX]

                                                                 31 Stems winged; plants erect.

                                                                     33 Disc flowers bright white; leaves unlobed or with 2 basal lobes

                                                                     33 Disc flowers creamy or pale yellow; leaves prominently pinnately lobed, with 5-many lobes

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

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

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

      4 Phyllaries tipped by a hooked spine

      4 Phyllaries not armed, herbaceous to the tip.

        5 Cypselae with 5 angles or 5 grooves; involucre 2-3 mm tall and in diameter; pappus of 1 (-5+) usually glandular setae (interpretable as bristles, hence keyed here); [Coastal Plain; FL and GA]

        5 Cypselae with 10 ribs; involucre 3.5-12 (-15) mm tall and in diameter; pappus of 35-40 barbellulate bristles; [mainly Coastal Plain; VA south to s. FL, west to e. LA]

          6 Heads larger, the involucre 6-15 mm high, with 15-40 phyllaries; leaves with conspicuous (at least at 10× magnification) resin dots.

          6 Heads smaller, the involucre 3.5-6 mm high, with 5-12 phyllaries; leaves without shining punctate glands (except punctate-glandular in Litrisa carnosa, of the FL peninsula).

             7 Stem with punctate glands; peduncles punctate-glandular and also hirsutulous; pappus bristles in 2 series; [of FL peninsula]

             7 Stem eglandular, glabrous or spreading-hirsute; peduncles glabrous or stipitate-glandular; pappus bristles in 1 series; [widespread in the Coastal Plain].

1 Receptacle epaleate (lacking receptacular bracts individually subtending flowers, but the receptacle sometimes bearing bristles, setae, hairs, or pits with laciniate margins; some taxa lacking paleae on many or most flowers of the head are keyed here as well, as a failsafe).

               8 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, except in species in which the phyllaries are radially winged); calyculus (of bracts subtending the phyllaries and differing from them in texture, color, or orientation) present or not; [tribe Senecioneae]

                 9 Annuals, 2-10 dm tall (or perennial, vining or sprawling and to 30 dm long in Gynura); leaves cauline and alternate; disc flowers orangey-brown, brick-red, purplish, yellow.

                   10 Plants perennial, vining or sprawling, velutinous or villous with purple hairs

                   10 Plants annual, upright or ascending, not purple-hairy.

                     11 Involucre subtended by several leafy bracts; cypselae 8- or 10-ribbed

                     11 Involucre not subtended by bracts; cypselae 5-ribbed

                 9 Perennials (robust annuals in Erechtites), 2-30 dm tall; leaves basally disposed and alternate on the stem (except only alternate in Erechtites); disc flowers cream or yellow (rarely pale lavender in Arnoglossum).

                       12 Plants annual, with leaves primarily on the stem; leaves sharply and raggedly toothed or even pinnately lobed; heads disciform (the outer flowers female, the middle bisexual, and the inner functionally male)

                       12 Plants perennial, with leaves basally disposed (larger basal leaves, decreasing in size upwards, the basal leaves sometimes withering late in the year); leaves with generally regular toothing, stem leaves sometimes pinnately lobed; heads discoid (all flowers bisexual)

                          13 Disc flowers yellow.

                            14 Perennials; leaves basally disposed, the basal or lower stem leaves unlobed (though toothed)

                            14 Annuals; leaves not basally disposed, evenly distributed on the stem, the lower stem leaves more-or-less pinnatifid

                          13 Disc flowers cream, white, or greenish white (to pale lavender in some Arnoglossum).

                              15 Phyllaries 5, radially wing-keeled or not; disc flowers 5; calyculus absent

                              15 Phyllaries 7-21, not radially winged; disc flowers 10-55 (-80+); calyculus absent or of 1-9+ bracts.

                                16 Plants (5-) 6-24 dm tall; calyculus of 4-9+ bracts; [collectively relatively widespread in our region]

                                16 Plants 1-7 dm tall; calyculus absent or of 1-5+ bracts; [Mountains of w. NC and e. TN]

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

                                  17 Stem prominently winged, the wings > 1 mm wide

                                  17 Stem not winged (sometimes the leaves decurrent < 2 cm down the stem from the node).

                                    18 Phyllaries usually 12-30+ in 3-10+ series, scarious (at least the margins).

                                       19 Plants perennial, mat-forming by stolons, with basal rosettes of spatulate leaves, these usually with obvious appressed hairiness on (at least) the lower and (sometimes also) the upper blade surfaces; erect stems (with scattered alternate leaves) 4-45 cm tall; plants usually dioecious (pistillate and staminate heads on separate plants)

                                       19 Plants annual, biennial, or perennial, not mat-forming or stoloniferous, erect, the leaves usually lanceolate or linear (spatulate in some species), leaf surface hairiness variable; erect stems (with alternate leaves) 5-80 cm tall; plants hermaphroditic (with heads containing both pistillate and functionally staminate flowers) or dioecious or subdioecious (in Anaphalis).

                                         20 Plants perennials; heads discoid (unisexual or nearly so); plants usually unisexual and dioecious

                                         20 Plants annuals (perennials in Omalotheca sylvatica); heads disciform (each bisexual); plants hermaphroditic.

                                           21 Leaves oblanceolate, 1.5-4 mm wide, notched at the tip or with a minute apiculus in the notch; pappus bristles persistent, plumose

                                           21 Leaves various in shape, the lager > 4 mm wide, acuminate, acute, obtuse or rounded at the tip; pappus readily falling, the bristles barbellate to barbellulate.

                                             22 Heads in capitate clusters arrayed in corymbiform or paniculiform arrays; phyllaries white or silvery; pappus bristles distinct, falling individually

                                               23 Pappus bristles connate basally into a ring, falling together

                                               23 Pappus bristles distinct, falling individually

                                             22 Heads in spicate arrays, or in glomerules axillary to leaves or well-developed bracts; phyllaries white to red-tinged or brown; pappus connate at the base into a ring, falling as a unit.

                                                 24 Perennial; phyllaries in 2-3 series; cypselas strigillose; involucre light to dark brown; [waif, in PA]

                                                 24 Annual; phyllaries in 3-7 series; cypselas papillate or glabrous; involucre white to red-tinged or brown; [widespread in our region]

                                                    25 Pappus of 12-28 bristles; cypsela faces papillate

                                                    25 pappus of 8-12 bristles; cypsela faces glabrous

                                    18 Phyllaries in 3-5 series, herbaceous to thickened, generally green in color.

                                                      26 Disc corollas yellow, pale yellow, orange, reddish, or brown.

                                                        27 Phyllaries 5, in one series; phyllaries streaked with elongate glands filled with strong-scented oil

                                                        27 Phyllaries 10-60+ in 2-9 series; phyllaries eglandular or with small punctate glands.

                                                          28 Phyllaries strongly armed with long spines

                                                          28 Phyllaries unarmed

                                                            29 Decumbent annual, to 2 dm tall; heads solitary and axillary

                                                            29 Erect or ascending annual or perennial, 1-15 dm tall; heads in corymbiform, paniculiform, or racemiform arrays.

                                                              30 Plants dioecious, either male or female; heads either staminate, with 10-50 flowers, or pistillate, with 20-150 flowers; heads pale yellow to white

                                                              30 Plants hermaphroditic; heads bisexual, with 2-35 flowers, either all perfect (bisexual), or a mixture of perfect (bisexual) and functionally staminate flowers.; heads yellow to pale yellow.

                                                                 31 Leaves entire; flowers 2-6 per head; heads arrayed in a neatly flat-topped corymb

                                                                 31 Leaves (at least the larger) toothed or lobed; flowers 5-35 per head; heads in racemiform, paniculiform, or corymbiform arrays, but if corymbiform, irregular.

                                                                   32 Larger leaves 1-5 cm long, < 1 cm wide; involucres 2-7 mm in diameter; [s. and se. TX].

                                                                     33 Inflorescences in rounded, corymbiform arrays; leaves glabrous

                                                                     33 Inflorescences in elongate, racemiform to paniculiform arrays; leaves moderately to densely hairy with both glandular and non-glandular hairs

                                                      26 Disc corollas pink, purple, lavender, blue, or white.

                                                                       34 Phyllaries either spine-tipped, or appendaged with a marginal zone that is strikingly different in color and texture than the phyllary body (except Leuzea); receptacle epaleate, but densely beset with bristles or subulate scales (flattened bristles).

                                                                         35 Phyllaries scarious-margined, neither spine-tipped nor appendaged with dentate or fringed appendages

                                                                         35 Plyllaries either spine-tipped or appendaged.

                                                                           36 Phyllaries tipped by a hooked spine

                                                                           36 Phyllaries appendaged, the appendage black, brown, tan, or scarious, and toothed or fimbriate.

                                                                              37 Phyllary bodies linear, their margins entire (phyllary appendages fimbriate; however); leaf margins entire, denticulate or serrulate

                                                                              37 Phyllary bodies oblong, ovate, or obovate, both their margins and appendages fimbriate; leaf margins entire, toothed, or pinnately lobed.

                                                                                38 Flower heads pink, lavender, or purplish; phyllary appendages scarious and spineless, decurrent along the phyllary margin nearly to the phyllary base; perennial; flowers pink to purple, flowering Jun-Oct

                                                                                38 Flowers heads blue; phyllary appendages not or only slightly decurrent along the phyllary margins; annual; flowers pale to medium blue, flowering Apr-Jun

                                                                       34 Phyllaries not armed, also not appendaged with a marginal zone that is strikingly different in color and texture than the phyllary body.

                                                                                  39 Plants dioecious, either male or female; heads either staminate, with 10-50 flowers, or pistillate, with 20-150 flowers; heads pale yellow to white

                                                                                  39 Plants hermaphroditic; heads bisexual, with 3-100+ flowers, either all perfect (bisexual), or a mixture of perfect (bisexual) and functionally staminate flowers.; heads purple, pink, lavender, or whitish.

                                                                                    40 Leaf blades orbicular; leaf margin scalloped or crenate; [rare waif in our region]

                                                                                    40 Leaf blades linear, lanceolate, or ovate; leaf margin entire, serrulate, or serrate; [collectively common and widespread].

                                                                                      41 Style branch appendages absent, the style branch stigmatic along the upper surface nearly to the tip; [tribe Vernonieae].

                                                                                        42 Pappus bristles in 1 series; heads disciform (the outer flowers of the head pistillate, the inner flowers of the head functionally staminate); leaf margins toothed; corollas white to cream or pink (rarely purple)

                                                                                        42 Pappus bristles in 2 series, the outer much shorter; heads discoid (all flowers bisexual and fertile); leaf margins toothed or entire; corollas purple or deep pink (rarely pale pink or white)

                                                                                      41 Style branch appendages deltate, lanceolate, or terete to clavate, the style branch various.

                                                                                           43 Style branch appendages deltate or lanceolate; style branches stigmatic along 2 lines from near the base to the attachment of the appendage; [tribe Astereae].

                                                                                             44 Disc flowers 8-20; pappus bristles in 2 series; [GA and Panhandle FL west to AL, GA, and LA]

                                                                                             44 Disc flowers 75-95+; pappus bristles in 1 series; [waif]

                                                                                           43 Style branch appendages terete to clavate; style branches "eupatorious", linear to slightly clavate-thickened at the tip, the stigmatic surface usually papillate; [tribe Eupatorieae]

                                                                                               45 All leaves entire (or at most with a few obscure crenations); phyllaries lacking elongate striations, the nerving not apparent.

                                                                                                 46 Heads borne in spiciform or racemiform arrays (all heads directly attached to a central access of the capitulescence)

                                                                                                 46 Heads borne in corymbiform, paniculiform, or thyrsiform arrays (at least some heads borne on secondary branches of the capitulescence.

                                                                                                   47 Involucres 2-3 mm tall; cypselas 5-ribbed

                                                                                                   47 Heads 3-20 mm tall; cypselas 10-ribbed.

                                                                                                     48 Heads 3.5-6 mm tall; phyllaries 5-12 in 1-2 (-3) series; [Coastal Plain, NC to FL to e. LA].

                                                                                                        49 Stem with punctate glands; peduncles punctate-glandular and also hirsutulous; pappus bristles in 2 series; [of FL peninsula]

                                                                                                        49 Stem eglandular, glabrous or spreading-hirsute; peduncles glabrous or stipitate-glandular; pappus bristles in 1 series; [widespread in the Coastal Plain].

                                                                                                     48 Heads 3-20 mm tall; phyllaries 15-50+ in 3-7 series; [collectively widespread].

                                                                                                          50 Heads borne in corymbiform arrays; involucres 6-12 (15) mm tall; receptacles paleate, at least towards the periphery of the receptacle; pappus of 35-40 barbellulate to barbellate bristles; [nearly restricted to the Coastal Plain]

                                                                                                          50 Heads borne in paniculiform or thyrsiform arrays; involucres 3-20 mm tall; receptacles epaleate; pappus of 12-40 coarsely barbellate, subplumose, or plumose bristles; [widespread in our region]