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; [tribe Digitaleae]

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

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

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

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

....3 Corolla with a slender spur at the base.

........5 Flowers in terminal racemes

........5 Flowers solitary in leaf axils.

..........6 Stems erect; leaves linear

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

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

............ 7 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.

............ ..8 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]

............ ....9 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]

............ ....9 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]

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

............ ......10 Leaves whorled.

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

............ ........11 Terrestrial; leaves 40-15 cm long, lanceolate or elliptic, toothed; [tribe Veroniceae]

............ ......10 Leaves opposite.

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

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

............ ............ 13 Calyx and corolla 4-merous.

............ ............ ..14 Leaves punctate; stamens 4; [tribe Gratioleae]

............ ............ ..14 Leaves not punctate; stamens 2; [tribe Veroniceae]

............ ............ 13 Calyx and corolla 5-merous.

............ ............ ....15 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].

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

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

............ ............ ....15 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).

............ ............ ........17 Stamens 2; [section Gratioleae].

............ ............ ..........18 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]

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

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

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

............ ............ ........17 Stamens 4.

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

............ ............ ............ ..20 Sepals distinct or very nearly so.

............ ............ ............ ....21 Leaves deeply pinnatifid; [tribe Stemodieae]

............ ............ ............ ....21 Leaves entire or toothed; [tribe Gratioleae].

............ ............ ............ ......22 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

............ ............ ............ ......22 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