1 Leaves alternate, at least those on the upper stem; calyx 5-merous; stamens 4.

  2 Corolla lacking a spur or pouch at the base

    3 Plants erect herbs, not vining; [tribe Digitaleae]

    3 Plants vining; [tribe Antirrhineae].

      4 Calyx glandular-pilose; corolla lacking a raised palate (the raised area of lower lip)

      4 Calyx glabrous; corolla with a raised yellow palate (the raised area of lower lip)

  2 Corolla with a distinct spur or broad pouch protruding between the 2 lower calyx lobes; [tribe Antirrhineae].

        5 Corolla with a broad pouch at the base (saccate or gibbose).

          6 Calyx lobes about equal, all shorter than the corolla tube; corolla 25-40 mm long; leaves to 15 mm wide

          6 Calyx lobes distinctly unequal, all longer than the corolla tube; corolla 10-13 mm long; leaves to 5 mm wide

        5 Corolla with a slender spur at the base.

             7 Flowers in terminal racemes

             7 Flowers solitary in leaf axils.

               8 Stems erect; leaves linear

               8 Stems prostrate; leaves orbicular, ovate, or triangular.

                 9 Leaves orbicular in outline, palmately lobed and veined; stems rooting at nodes

                 9 Leaves ovate or triangular, pinnately veined; stems not rooting

1 Leaves either strictly basal, or opposite or whorled throughout; calyx 0-, 4-, or 5-merous; stamens 1, 2, or 4.

                   10 Leaves strongly basally disposed, usually all the leaves basal (or with significantly reduced cauline leaves); petals 3 or 4, scarious and translucent in texture or otherwise dull-yellow and inconspicuous; inflorescence a spike; [tribe Plantagineae]

                     11 Plants with leaves usually all basal; petals scarious and translucent in texture, not bilabiate; fruit a circumsessile dehiscent capsule (i.e. a lid-bearing pyxide); [collectively widespread]

                     11 Plants with prominent basal leaves and reduced, sub-whorled, cauline leaves; petals yellow, bilabiate; fruit a loculicidal capsule; [s. OH w. to s. IL, northward]

                   10 Leaves cauline, either opposite or whorled; petal 0, or 4, or 5; inflorescence various.

                       12 Leaves whorled.

                          13 Aquatic; leaves 5-30 mm long, lanceolate, toothed to deeply dissected into linear segments; [tribe Gratioleae]

                       12 Leaves opposite.

                            14 Petals 0; sepals 0, stamens 1; leaves both < 2 cm long and entire; [tribe Callitricheae]

                            14 Petals 4 or 5; sepals 4 or 5; stamens 2 or 4; leaves > 2 cm long, or serrate, or both.

                              15 Calyx and corolla 4-merous.

                                16 Leaves punctate; stamens 4; [tribe Gratioleae]

                                16 Leaves not punctate; stamens 2; [tribe Veroniceae]

                              15 Calyx and corolla 5-merous.

                                  17 Plants erect, moderately robust, usually > 4 dm tall, larger leaves > 5 cm long; inflorescences terminal (the bracts subtending flowers strongly reduced in size in comparison to main leaves of the stem); [tribe Cheloneae].

                                    18 Inflorescence compact, the inflorescence axis generally hidden by the closely packed and overlapping flowers; each flower subtended by large overlapping bracts

                                    18 Inflorescence more diffuse, the inflorescence axis readily visible between the flowers; flowers lacking extra subtending bracts

                                  17 Plants creeping, decumbent or erect, small, usually < 4 dm tall (except Mecardonia, to 5 dm tall), larger leaves < 5 cm long; inflorescences axillary (all or most of the flowers axillary to more-or-less normally sized leaves).

                                       19 Stamens 2; [section Gratioleae].

                                         20 Capsule flattened, compressed in ×-section; capsule wider than long, notched; leaves dimorphic, with narrow submersed leaves on the lower stems, and broad floating leaves just subtending the aerial inflorescences; [of vernal pools on granite outcrops in Piedmont SC, GA, and AL]

                                         20 Capsule turgid, roundish in ×-section; capsule longer than wide; leaves monomorphic; [collectively of many habitats and widespread].

                                           21 Flowers and fruits on definite pedicels; annual or perennial; leaves not papillose

                                           21 Flowers and fruits sessile or subsessile, the pedicels < 1 mm long; perennial; leaves papillose on the surfaces and margins

                                       19 Stamens 4.

                                             22 Sepals evidently connate into a tube about as long as the lobes; [section Cheloneae]

                                             22 Sepals distinct or very nearly so.

                                               23 Leaves deeply pinnatifid; [tribe Stemodieae]

                                               23 Leaves entire or toothed; [tribe Gratioleae].

                                                 24 Corolla nearly radially symmetrical; corolla lobes about as long as the corolla tube; leaves palmately veined, with parallel veins diverging from the base, margins entire to crenulate; of aquatic to moist habitats, often somewhat succulent

                                                 24 Corolla distinctly bilabiate; corolla lobes shorter than the corolla tube; leaves pinnately veined, with a single main-vein and lateral veins diverging along it, margins serrate; of moist habitats, not succulent

1 Cauline leaves palmately compound.

  2 Cauline leaves essentially sessile, and also palmately cleft to the base, and further lacerately divided into linear or oblanceolate segments

  2 Cauline leaves petiolate, with 3-5, sessile or petiolulate, ovate, elliptic, or obovate leaflets (these serrate and sometimes with additional lobes).

    3 Inflorescence a spherical umbel of many flowers; fruit a drupe with 2-3 seeds; stem leaves 3-5

      4 Leaflets 3 (-5), sessile or subsessile, the petiolules 0-3 mm long; larger leaflets 4-8 cm long, 0.5-2.5 cm wide, averaging about 2.5× as long as wide, the apex obtuse to acute; fruit yellow-green when ripe, longitudinally winged and ribbed in ×-section; petals white (rarely tinged with pink); inflorescence nodding in bud; underground storage organ a spherical tuber

      4 Leaflets (3-) 5, petiolulate, the petiolules (7-) 10-25 mm long; larger leaflets 6-15 cm long, 3.5-7 cm wide, averaging about 1.8× as long as wide, the apex acuminate; fruit bright red when ripe, smoothly elliptical in ×-section; petals light green; inflorescence erect in bud; underground storage organ an +/- elongate root, this vertical or horizontal, and sometimes branched

    3 Inflorescence of single terminal flowers on the 1-several branches; fruit an aggregate of achenes; stem leaves 3

1 Cauline leaves simple.

        5 Inflorescence an involucrate head subtended by phyllaries, heads solitary or many, variously arrayed in secondary inflorescences; fruit a cypsela

        5 Inflorescence various, but not as above; fruit various, not as above (sometimes the flowers tightly grouped, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).

          6 Fruit a 3-lobed, 3-locular capsule; inflorescence a cyathium, consisting of a single pistillate flower (reduced to a single 3-carpellate pistil) and 2 or more staminate flowers (each reduced to 1 stamen), borne in a cup-like involucre, the involucre bearing pointed or rounded glands, these sometimes brightly colored and petaloid, mimicking an individual flower (the cyathia then secondarily arranged in terminal cymes, or solitary and axillary, etc.); fresh plants with milky juice

          6 Fruit various, not as above; inflorescence not a cyathium (and staminate or bisexual flowers almost always with > 1 stamen); fresh plants lacking milky juice.

             7 Leaves succulent, the terminal whorls closely juxtaposed; pistils 4-5; fruit an aggregate of follicles

             7 Leaves herbaceous, thin in texture, whorls separated; pistil 1, of 2-5 fused carpels; fruit a capsule, achene, or drupe.

               8 Larger whorled leaves on a plant < 10 mm wide [some taxa keyed here and under the second lead].

                 9 Inflorescence a cymule, either axillary, or axillary and terminal; ovary inferior.

                   10 Leaves markedly variable in shape or size in each whorl; fruit a capsule; petals 5

                   10 Leaves similar in size and shape in each whorl; fruit dry or fleshy, indehiscent; petals (3-) 4

                 9 Inflorescence a terminal raceme, panicle, spike, cyme, corymb, or umbel; ovary superior.

                     11 Corolla bilaterally symmetrical, the petals connate; carpels 2; stamens 4, 6, or 8.

                       12 Stamens 4; corolla blue or almost white

                       12 Stamens 6 or 8; corolla pink or yellow

                     11 Corolla radially symmetrical, the petals separate; carpels 2, 3, or 5; stamens 5, 10, or many.

                          13 Inflorescence an axillary umbel; leaves narrowly linear and more than 10× as long as wide, > 20 mm long and < 2 mm wide; whorls of 3-6 leaves

                          13 Inflorescence a terminal cyme, raceme, panicle, or umbel; leaves as above, or broader in shape, narrower, or shorter; whorls of 3-16 leaves.

                            14 Inflorescence a terminal cyme or umbel; corolla white; carpels 5.

                              15 Leaves narrowly linear, 12-16 in each whorl; stamens 5

                              15 Leaves ovate or obovate, 3 (-4) in each whorl

                            14 Inflorescence a terminal raceme or panicle; corolla reddish, maroon, or yellow.

                                16 Corolla reddish or maroon

                                16 Corolla yellow

               8 Larger whorled leaves on a plant > 10 mm wide.

                                  17 Inflorescence a spike; perianth absent; fruit a drupe

                                  17 Inflorescence various, but not a spike; perianth present; fruit various, but not a drupe.

                                    18 Inflorescence of terminal involucrate clusters; perianth of 6 tepals; fruit an achene; stamens 9; [plants of very dry habitats]

                                    18 Inflorescence various, but not as above; perianth of 2 whorls (the calyx often obsolete in Galium in RUBIACEAE), 3-, 4-, 5-, 6-, or 7-merous; stamens 2-7; [plants of dry-mesic to very wet habitats].

                                       19 Fruit dry or fleshy, indehiscent; petals (3-) 4; ovary inferior

                                       19 Fruit a capsule or follicle, dehiscent; petals 4-7; ovary superior.

                                         20 Inflorescence an umbel; fresh plants with milky juice

                                         20 Inflorescence not an umbel; fresh plants with clear juice.

                                           21 Corolla pink-purple, 6-merous, the petals separate and borne on the edge of a hypanthium; stamens 8, 10, or 12; [plants of wetlands]

                                           21 Corolla white, yellow, or greenish, 4-, 5-, or 7-merous, the petals fused at least basally into a tube (falling as a unit), not on a hypanthium; stamens 2, 4, 5, or 7; [plants of mesic habitats].

                                             22 Stamens 4, 5, or 7; corolla radially symmetrical.

                                               23 Petals yellowish-white, with prominent green streaks; biennial or monocarpic plant, 10-30 dm tall when fertile; leaves 15-35 cm long

                                               23 Petals white or yellow; perennial plants, 1-15 dm tall; leaves 1-15 cm long.

                                                 24 Leaves punctate; stem without swollen nodes

                                                 24 Leaves not punctate; stem with swollen nodes