1 Inflorescence unbranched, the heads solitary on peduncles from the leaf axils of the prostrate to erect stem.

  2 Leaves pinnately lobed or dissected; [waif]

  2 Leaves entire, irregularly toothed (rarely with some minor, irregular lobing).

    3 Heads subglobose or hemispherical when fully developed, about as wide as long; bracts subtending the head barely extending beyond the base of the head; main stems leaves linear, narrowly elliptic, narrowly oblanceolate, sometime tricuspid apically

    3 Heads cylindrical, longer than wide; bracts subtending the head longer than the radius of the head, thus extending conspicuously beyond the base of the head; main stem leaves elliptic, broader than above

1 Inflorescence branched, the heads in a cyme borne terminally on the erect or prostrate stem.

      4 Basal and cauline leaves (all, or at least many of the cauline) definitely deeply lobed into 3 or more divisions, < 10 cm long; leaf lobes tipped with moderately stiff to very stiff spine tips.

        5 Leaves herbaceous to stiff, green to slightly glaucous, pinnately toothed or lobed.

          6 Heads blue purple or sometimes reddish; basal leaves serrate but not divided.

             7 Heads 20-35 mm tall, purple to reddish; heads capped with conspicuous (1-2 cm long) spinescent bracts

             7 Heads 4-15 mm tall, bluish to purplish; heads capped with a few, mostly entire, spinescent bracts, or lacking them.

               8 Plants erect, stem solitary, branching upwards; fruits 1-2 mm long

               8 Plants diffuse, decumbent, branched from the base and upwards; fruits 1.5-3 mm long

                 9 Cauline tips absent; mericarps 1.5-2 mm long

                 9 Cauline leaves present, spine tipped; mericarps 2.5-3 mm long

          6 Heads greenish, whitish, or pale lavender; basal leaves pinnately or pinnately-ternately divided.

                   10 Plants stout, fleshy, usually glaucescent; basal leaves 10-25 cm long and wide, pinnately or pinnate-ternately divided into > 7 segments, the cauline leaves similar but reduced in size and number of divisions; heads 10-15 mm in diameter; [rare ballast waif of disturbed ground]; [subgenus Eryngium]

                   10 Plants slender, not fleshy, green; basal and cauline leaves 2-6 cm long, 3-5 (-7) pinnately parted; heads 5-8 mm in diameter; [native species of dry pinelands or scrub of the Coastal Plain of e. GA, s. AL, and FL].

                     11 Basal leaves pinnately lobed; stems decumbent at base, ascending (the mature plant often wider than it is tall); stems leafy throughout their length, usually with 10 or more leaves; [dry pinelands and scrub of the Coastal Plain of e. GA, s. AL, and FL]

                     11 Basal leaves trilobed; stems ascending at base (the mature plant taller than wide); stems erect, unbranched; stems sparsely leafy, especially upwards, usually with 7 or fewer leaves; [endemic in Florida scrub in Highlands County, c. peninsular FL]

      4 Basal and cauline leaves unlobed (except sometimes the uppermost; note that bracts in the inflorescence are often lobed), 3-100 cm long; leaf margins without coarse spine-tips (finely spinulose in E. foetidum).

                       12 Basal leaves evenly and rather finely toothed with spine-tipped teeth

                       12 Basal leaves with entire or crenate margins, lacking spiny tips (though in some species with flexible bristles along the margins).

                          13 Blades of basal and lower cauline leaves 10-100 cm long, acuminate to acute apically, clasping basally, with a length/width ratio of 5-50.

                            14 Leaves with primary veins pinnate-reticulate, with or without marginal bristles; flowers blue.

                              15 Styles 3.0-4.0 mm long at maturity, scarcely exceeding the bractlets (which subtend each flower); heads subglobose to hemispherical, 6-12 mm in diameter; middle cusp of the bractlets elongate, distinctly longer than the lateral cusps

                              15 Styles 4.0-6.0 mm long at maturity, exceeding the bractlets; heads globose, 9-15 mm in diameter; middle cusp of the bractlets about equal in length to the lateral cusps

                            14 Leaves with primary veins parallel, with marginal bristles; flowers greenish-white.

                                16 Larger leaves < 1.5 cm wide; marginal bristles in fascicles of 1-3 (-4), those on the lower portion of the leaf usually in fascicles of 2-3

                                16 Larger leaves > 1.5 cm wide; marginal bristles of leaves solitary

                                  17 Plant green; marginal bristles triangular (broadened at the base); flowering late

                                  17 Plant glaucous; marginal bristles acicular; flowering early

                          13 Blades of basal and lower cauline leaves 3-7 (-10) cm long, acute to obtuse apically, cordate to truncate basally, with a length/width ratio of 1.5-3 (-6)

                                    18 Heads ovoid, taller then wide; [non-native from horticultural use]

                                    18 Heads hemispheric, about as wide as high; [native, seeps, bogs, and wet pine savannas, VA, KY, AR, and OK southwards]

                                       19 Bracts of terminal whorl pinnately 3-7-lobed, lobes linear to filiform; mid-culm blades narrowly lanceolate to linear, (5.5-) 6.2-15 (-18)× as long as wide; leaf margins remotely serrate (1-4 teeth per cm at midlength), teeth sharp, irregular, sometimes spinose; stems slender, wiry; [w. Gulf Coastal Plain, or Inner Coastal Plain of GA].

                                         20 Mid-stem blades 2.3-3.5cm (x̄ = 3.0cm), usually with long spinose teeth basally; stems often flexuous and diffusely branching from near base; [e of the Mississippi River; GA]

                                         20 Mid-stem blades (3.2-) 4.1-5.9 (-8.9) cm (x̄ = 5.2cm), serrate to shortly spinose-serrate; stems erect, mostly single, branched above (branched throughout in robust plants of E. lanceolatum, then with stout, erect stems); [w of the MS River; LA, AR, TX].

                                           21 Leaves mostly deltate-lanceolate, widest near base, (0.7-) 0.9-1.6 (-1.8) cm wide; leaf teeth (3-) 4-6 per cm at mid-length, regularly serrate or dentate (uppermost sometimes ±spinose-serrate)

                                           21 Leaves mostly linear-lanceolate, widest at about 1/3-1/2 length, 0.3-0.8 (-1.2) cm wide; leaf teeth (1-) 2-3 (-4) per cm at mid-length, remote, varying from crenate-serrate (lower leaves) to spinose-serrate

                                       19 Bracts of terminal whorl 3-(-5)-lobed basally or unlobed, serrate, lanceolate to ovate; mid and upper cauline leaves mostly ovate to lanceolate, (1.5-) 2-3 (-4)× as long as wide; leaf margins serrulate to crenate-dentate (3-8 teeth per cm at mid-length), teeth frequently blunt or rounded; stems stout to slender, erect; [collectively widespread].

                                             22 Bracts of terminal whorl finely serrate, teeth (5-) 7-14 (-19) per side, ovate or elliptic; cauline leaves ovate to elliptic, (1.6-) 2-4.3 (-4.4) cm wide at mid-stem, serrulate (teeth >25 per side); plants robust, the stems stout, the heads commonly 20--50+; [inner Gulf Coastal Plain, Sedimentary Appalachians, and Piedmont]

                                             22 Bracts of terminal whorl 3-lobed (or coarsely toothed), the terminal lobe with 1-3 (-6) additional teeth per side, lanceolate to linear; cauline leaves mostly lanceolate or narrowly elliptic-ovate, (0.7-) 0.9-1.8 (-2.1) cm wide at mid-stem, serrate or crenate-serrate (teeth (6-) 9-22 (-26) per side, rarely more in E. lanceolatum); plants smaller, the stems slender to moderately stout, the heads usually <25; [bogs and seepage slopes, mostly Coastal Plain, rarely Piedmont and Mountain bogs].

                                               23 Mid-stem blades deltate-lanceolate, (3.4-) 4-6 (-6.7) × as long as wide, regularly serrate with small straight-sided teeth; petioles (1.6-) 1.9-2.9 (-3.6) cm, spreading; [west of the MS River]

                                               23 Mid-stem blades blades elliptic-ovate, 2-3 (-3.7)× as long as wide, sharply serrate (teeth curved or acuminate) to crenate-serrate; petioles (0.8-) 0.9-1.6 (-1.9) cm at mid-culm, usually sheathing the stem for most of their length; [east of the MS River].

                                                 24 Mid-stem blades sharply serrate, teeth 12-22 (-26) per side; bracts of terminal whorl with irregular long teeth (or weakly 3-parted), teeth (3-) 4-6 (-8) per side (ignore 2º and 3º bracts); leaves and inflorescence branches often lax; [NC, SC; upper Piedmont and low Mountains]

                                                 24 Mid-stem blades sharply serrate to shallowly crenate-serrate, teeth (6-) 9-12 (-14) per side; bracts of terminal whorl tricuspidate, central lobe with an additional 1-2 (-4) teeth per side (rarely merely coarsely serrate in var. maficolum); leaves and inflorescence branches stiff; [of the Coastal Plain from VA to w. LA, or of the Blue Ridge Mountains of NC and GA].

                                                    25 Basal leaves (withering by flowering) flat against soil surface, broadly ovate-elliptic or ovate, obscurely crenate in lower half to subentire; teeth of midstem leaves teeth usually rounded to bluntly acute (edges forming a 45-75º angle, the outer strongly convex); inflorescence branches spreading-ascending; [plants of the Coastal Plain from VA to e. LA, over acidic substrates]

                                                    25 Basal leaves (withering by flowering) typically ascending, obovate to narrowly ovate-elliptic, often serrate to near apex; teeth of midstem leaves slender, acuminate (edges forming a ~15-30º angle); inflorescence branches erect; [plants of Mountain bogs of NC and GA, usually over mafic substrates]

1 Leaves linear, lanceolate, or oblancolate, > 4× as long as wide.

  2 Leaves phyllodial (septate, hollow or flat, segmented); flowers white or purple; [plants of wetlands].

    3 Umbels simple; leaves spatulate, broader towards the tip, often somewhat flattened in ×-section, rounded or obtuse at the apex

    3 Umbels compound; leaves tapering to a pointed tip, either flat or terete in ×-section.

      4 Leaves flat in ×-section, with obvious parallel venation and less obvious septae / cross-partitions

      4 Leaves terete in ×-section, the septae obvious.

        5 Plants 1-11 dm tall, annuals, sometimes mat-forming and adventitiously perennial; fruits 1-3 mm long, with lateral ribs; rays 3-15

        5 Plants 6-24 dm tall, perennials from rhizomes or tubers; fruits 4-9 mm long, with lateral wings; rays 5-20

  2 Leaves “normal” (non-septate, flat, continuous, and in some cases lobed, toothed, or spinose-margined); flowers blue, yellow, white, or whitish-green; [plants of wetlands or uplands].

          6 Flowers borne in involucrate heads; corolla blue or greenish-white

          6 Flowers in compound umbels; corolla yellow or white.

             7 Stem leaves similar to the basal, all simple; corollas yellow; [exotic, of disturbed areas]

             7 Stem leaves palmately 3-5-foliolate with linear leaflets, differing from the simple basal leaves; corollas white; [native, of blackland prairies and associated disturbed areas, from AL and TN westward]

1 Leaves orbicular, ovate, or elliptic, < 4× as long as wide.

               8 Leaves orbicular, about as wide as, or wider than, long; base peltate or cordate.

                 9 Leaves herbaceous or somewhat fleshy. toothed or lobed, but not spinose; inflorescence umbellate or verticillate; flowers white, greenish, or purplish; [collectively common and widespread].

                   10 Foliage and fruits (or ovaries) stellate-pubescent or glochidiate; leaves lobed, but otherwise entire; [rare exotic]

                   10 Foliage and fruits (or ovaries) glabrous; leaves toothed, sometimes also lobed; [common natives and exotics]

               8 Leaves ovate or elliptic, 1.2-4× as wide as long; base cordate, peltate, or truncate.

                     11 Leaves perfoliate; flowers yellow; [rare exotics].

                       12 Stem leaves entire; umbellets subtended by broad foliaceous bractlets

                       12 Stem leaves serrate; umbellets lacking bractlets

                     11 Leaves cordate or truncate at the base; flowers white, green, yellow, blue, or purple;

                          13 Flowers greenish or blue; leaves all simple (sometimes stem leaves lobed); inflorescence a head or very congested (subcapitate) umbel; [plants of wetland situations, prostrate, creeping, or erect].

                            14 Inflorescence a very congested (subcapitate) umbel, with 4-9 flowers; leaves cordate at the base, long-petiolate, the petioles characteristically 2× as long as the leaf

                            14 Inflorescence a head, with > 20 flowers; leaves cuneate to truncate at the base, sessile to short petiolate, the petioles < 1× as long as the leaf (except E. prostratum)

                          13 Flowers yellow or purple; basal leaves simple, stem leaves usually compound; Inflorescence a compound umbel; [erect plants of upland situations].

                              15 Fruits (partly to fully mature) with thin-edged wings; flowers yellow or purple; central flower of each umbellet staminate and pedicelled; fruits all pedicelled in all umbellets

                              15 Fruits ribbed (with rounded, cordlike ribs), lacking thin-edged wings; flowers yellow; central flower of each umbellet either staminate and pedicelled, or pistillate and sessile; fruits all pedicelled in some umbellets (those with a staminate central flower), or the central fruit sessile in some umbellets (those with a pistillate central flower)