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

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

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

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

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

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

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

        5 Flowers in compound umbels; corolla yellow or white.

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

          6 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.

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

               8 Leaves leathery, with spinose margins; inflorescence a head; flowers blue; [rare introduction]

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

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

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

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

                   10 Leaves perfoliate; flowers yellow; [rare aliens].

                     11 XXXX

                     11 YYYY

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

                       12 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].

                          13 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

                          13 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)

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

                            14 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

                            14 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)

1 Leaves thread-like or quill-like, about as thick as wide.

  2 Plants bulbous at base, and with the leaf bases expanded and containing sporangia; plant tufted or with very short rhizomes; [Lycophytes]

  2 Plants either somewhat bulbous or not at the base, the leaf-bases not containing sporangia; plant rhizomatous; [Pteridophytes, Eudicots, Monocots].

    3 New leaves unfurling with circinate vernation (a fiddlehead); plants reproducing by spores, from sporocarps on short stalks from the rhizome; [Pteridophytes]

    3 New leaves lacking circinate vernation; plants reproducing by flowers and seeds.

      4 Perianth differentiated, with either 3 sepals and 3 petals or 5 sepals and 5 petals; stamens either 7-many or stamens 4.

        5 Sepals 3; petals 3; stamens 7-many; [Monocots]

        5 Sepals 5; petals 5; stamens 4; [Eudicots]

      4 Perianth undifferentiated, with 0, 3, or 6 tepals; stamens 1, 2, or 3; [Monocots].

          6 Gynoecium of 2 or more pistils, each pistil with 1 carpel and with 1 stigma

          6 Gynoecium of 1 pistil, each pistil with (2-) 3 carpels and (2-) 3 stigmas.

             7 Fruit an achene; perianth absent

             7 Fruit a capsule; perianth of 6 tepals

1 Leaves ribbon-like or strap-like, distinctly flattened (sometimes only near the tip of the leaf).

               8 Subterranean portions of plant bearing bladder-traps; flowers yellow or purple, bilaterally symmetrical

               8 Subterranean portions of plant lacking bladder traps; flowers white, green, gray, radially symmetrical (except bilaterally symmetrical in Glossostigma in PHRYMACEAE).

                 9 Leaves broadened towards the tip; [Monocots, Eudicots].

                   10 Flowers 3-merous; [Monocots]

                   10 Flowers 4- or 5-merous; [Eudicots].

                     11 Leaves not phyllodial; leaves opposite

                 9 Leaves parallel-margined or tapering towards the apex over much of their length; [Monocots].

                       12 Leaves tapering towards the apex over much of their length; plant either tufted and not rhizomatous, or short rhizomatous;.

                          13 Plant tufted, not rhizomatous; leaves spreading radially; inflorescence a tightly button-like head of very numerous small flowers, white, gray, tan, yellowish, or blackish; roots thickened, septate (not requiring magnification), unbranched

                          13 Planted short-rhizomatous; leaves distichous, equitant; inflorescence either a subglobular, ovoid, or cylindrical head, of spirally imbricate scales, or a diffuse corymb; roots not thickened, not septate, branched.

                            14 Inflorescence a diffuse corymb; rhizomes and roots bright red

                            14 Inflorescence a subglobular, ovoid, or cylindrical head of spirally imbricate scales subtending individual flowers; rhizomes and roots not bright red

                       12 Leaves parallel-margined; plant usually rhizomatous.

                              15 Plants of marine habitats, growing submersed in salt water; [FL and the Gulf Coast of AL, MS, and LA]

                              15 Plants of freshwater or slightly to somewhat brackish habitats; [collectively widespread].

                                16 Leaves lacking any midvein; flowers and fruits in globose heads

                                16 Leaves with a midvein; flowers and fruits solitary or in diffuse inflorescences.

                                  17 Leaves with a distinct, broad lacunar band along the midvein

                                  17 Leaves lacking a distinct lacunar band along the midvein.

                                    18 Stamens 3

                                    18 Stamens >6