Plantaginaceae is the correct name for the family that encompasses not only the plantains with their reduced flowers, but also the related larger-flowered genera formerly placed in the Scrophulariaceae as well as highly reduced aquatics, such as Hippuris (in Hippuridaceae in Michigan Flora) and Callitriche (in Callitrichaceae in Michigan Flora).
1. Flowers tiny, lacking a corolla, or corolla regular and scarious.
2. Leaves in a basal rosette.
3. Leaves terete (ca. 3 mm or less thick at the middle, thence tapering to apex), at most 1-veined, glabrous; flowers unisexual (the staminate long-stalked, the pistillate basal); fruit indehiscent; submersed or on moist shores.
3. Leaves flat, in most species with at least 3 prominent veins and/or pubescent; flowers bisexual (in heads or spikes); capsule circumscissile; dry or rarely wet habitats.
Plantago (in part)
2. Leaves opposite or whorled on an elongate stem.
4. Leaves in whorls of 6–12 (usually 9).
4. Leaves opposite.
5. Flowers solitary in the leaf axils; corolla absent.
5. Flowers numerous in short, peduncled spikes; corolla present, scarious.
1. Flowers usually conspicuous, with both calyx and corolla present, the corolla petaloid, usually conspicuously bilaterally symmetrical.
6. Cauline leaves all or mostly alternate on fertile stems (lowermost leaves sometimes opposite and rosette of larger basal leaves sometimes present).
7. Corolla nearly regular, the lobes equaling or exceeding the tube.
Veronica (in part)
7. Corolla bilaterally symmetrical, ± 2-lipped, the lobes distinctly shorter than the tube (including spur, if any).
8. Stem trailing or sprawling; leaf blades not over 1.5 times as long as broad; corolla with basal spur; capsules ± spherical, ca. 3–4.5 mm in diameter.
9. Stem, leaves, and calyx glabrous; leaf blades palmately veined and lobed or scalloped; seeds with thin raised reticulate ornamentation.
9. Stems, leaves, and calyx pilose; leaf blades pinnately veined, usually hastate (1–2 pairs of small basal lobes); seeds covered with dense convolute-rounded ornamentation.
8. Stem erect; leaf blades (or their principal lobe) over 1.5 times as long as broad; corolla spurred (Chaenorhinum, Linaria) or not; capsules various, mostly longer than broad.
10. Corolla with a slender basal spur projecting back between the lower calyx lobes.
11. Flowers all solitary in axils of leaves (nearly to base of plant); corolla pale purple and white; leaves, calyx, and stem with ± dense gland-tipped hairs.
Chaenorhinum (in part)
11. Flowers in compact or elongate terminal inflorescences (ca. half or less the height of the plant); corolla yellow, red, or blue; leaves, calyx, and usually stem glabrous and eglandular or nearly so.
12. Corolla ca. 1.3–4 (–4.3) cm long (including spur), yellow (red-pink in a rare weedy annual); seeds strongly wrinkled, tuberculate, ridged, or winged.
12. Corolla 0.6–1.1 cm long, blue; seeds smooth or weakly pebbled.
10. Corolla without spur (at most swollen or saccate at base).
13. Corolla ca. half or more covered by the calyx.
13. Corolla much less than half covered by the calyx.
14. Leaves at least remotely crenate or toothed; corolla symmetrical (not swollen) at base, fully open at the throat.
14. Leaves entire; corolla swollen at base, closed at the throat by the palate.
15. Corolla at least 2.5 cm long, much exceeding the broadly ovate calyx lobes.
15. Corolla not over 1.5 cm long, barely if at all exceeding the linear calyx lobes.
6. Cauline leaves all or mostly opposite (rarely whorled) on fertile stems (may be alternate beneath flowers).
16. Inflorescence terminal and branched (± paniculate); stamens 4 fertile plus 1 staminodium.
16. Inflorescence a spike or raceme (no branched stalks), or flowers all axillary; stamens 2 or 4 fertile, in most genera with no staminodium (or only a very rudimentary one).
17. Leaves (especially middle and lower ones) deeply pinnately toothed or lobed ca. 1/3 or more the distance to the midrib.
17. Leaves of main stem toothed or entire but not so deeply pinnately toothed or lobed (uppermost leaves or bracts may have small basal lobes).
18. Sepals (at least at anthesis) fused ca. one-third or more the length of the calyx; fertile stamens 4.
18. Sepals separate nearly or quite to the base; fertile stamens 2 or 4.
19. Corolla ca. 2.3–3.5 cm long; sepals broadly ovate-orbicular, overlapping; stamens 4 fertile plus a filamentous elongate staminodium.
19. Corolla less than 1.5 cm long; sepals linear-lanceolate to somewhat ovate, not conspicuously overlapping; stamens 2 or 4 (including any staminodia).
20. Corolla with a spur projecting back at the base; plant with ± dense gland-tipped hairs; leaves linear; fertile stamens 4.
Chaenorhinum (in part)
20. Corolla not spurred; plant glabrous or with eglandular hairs (or if with gland-tipped hairs, the leaves not linear); fertile stamens 2 (staminodia filamentous, reduced, or none).
21. Leaves in whorls of 3–6 (–7), sharply toothed; inflorescence of 1–several dense elongate slenderly tapering spikes or spike-like racemes; corolla tube much longer than the lobes.
21. Leaves opposite, entire or toothed; inflorescence racemose or flowers solitary in axils of alternate or opposite bracts or leaves; corolla tube various.
22. Corolla 2-lipped, the tube much longer than the lobes; flowers solitary in axils of opposite leaves; sepals 5.
22. Corolla often nearly regular, the tube shorter than the lobes (usually a flat limb); flowers in axillary racemes or solitary in axils of bracts or leaves; sepals 4.
Veronica (in part)