Except for V. austriaca, V. chamaedrys, V. longifolia, and V. officinalis, which are rather conspicuous perennial escapes from cultivation, these are mostly unprepossessing plants with tiny flowers. Yet, en masse even the smallest plants can present a striking scene of blue when in full bloom. Some species have white rather than blue corollas, and in some, especially V. scutellata, the corolla is often a shade of pink.
The fruit is flattened and ± heart-shaped (or at least notched at the apex). The style is usually readily visible on nearly mature fruit, when it often provides useful key characters, although there are sometimes exceptions to the customary lengths, in both actual measurements and relation to the two capsule lobes between which the style arises. Some species have what definitely appear to be racemes, with distinctly pediceled flowers; others have more spike-like inflorescences, with very short pedicels. Again, measurements may be less discriminating than one would like. Pedicels near the base of an inflorescence tend to be longer (mature earlier) than those toward the apex of the stem, and the mature pedicels should be examined when their length must be known. In the species with a single terminal inflorescence, over half the plant may be occupied by flowers, whether one interprets them as being in a spike or raceme or as solitary in the axils of leaves. The real cauline leaves are opposite, but flowers usually arise from the axils of alternate leaves (or bracts, depending on their gradation in size and one’s definitions). Albach et al. (2004), show that Veronica is not a natural group, and suggest the solution to be broadening the genus to include Besseya (and other genera occurring outside of Michigan). Perhaps a better solution would be more division of Veronica to allow continued recognition of distinctive entities such as Besseya.
1. Flowers (and fruits) in definite racemes on peduncles arising mostly from axils of ordinary opposite or whorled foliage leaves (sometimes terminal in V. longifolia, with sharply toothed leaves), with bracts at base of pedicels extending distinctly less far than the flowers and much smaller than the foliage leaves; perennial.
2. Stem below the inflorescence at least minutely pubescent with eglandular hairs.
3. Blades of principal cauline leaves 2.5–8 times as long as broad, with numerous sharp teeth; tube of corolla nearly or quite as long as the lobes.
3. Blades of principal cauline leaves ca. twice or less as long as broad, entire to crenulate or shallowly toothed; tube of corolla very much shorter than the lobes.
4. Leaf blades entire or shallowly crenulate, glabrous.
V. serpyllifolia (in part)
4. Leaf blades definitely toothed, hairy beneath (and often above).
5. Pedicels up to 2.5 mm long (in fruit); corollas (when the limb is spread flat) ca. 5–8 mm broad or less; calyx 1.7–3.5 mm long; hairs on capsule ± dense, mostly gland-tipped.
5. Pedicels (2–) 2.5–7.5 mm long (in anthesis and fruit); corollas ca. (9–) 10–14 mm broad; calyx 3.5–5.5 mm long; hairs (if any) on capsule without glands.
6. Capsule ± elliptic, as long as broad or slightly longer; calyx lobes broadest well below the middle; pubescence ± evenly distributed around the stem below the nodes; stems stiff and upright, over 3 dm tall.
6. Capsule broadly obcordate, distinctly broader than long; calyx lobes broadest at or above the middle; pubescence much denser in 2 lines below the nodes; stems slender, prostrate, with ascending shoots up to 3 dm tall.
2. Stems glabrous or with some gland-tipped hairs (rarely with eglandular pubescence in V. scutellata, with very narrow leaves under 1 cm wide and 6–20 times as long as wide).
7. Leaves sessile, linear-lanceolate, not over 1 cm broad and ca. (6–) 8–20 times as long as broad, entire or remotely denticulate; mature pedicels reflexed, mostly (2–) 2.8–6 times as long as the bracts at their base; calyx 2–3.5 mm long, shorter than the mature fruit; racemes all or mostly alternate (arising in the axil of only one of any pair of opposite leaves).
7. Leaves petioled or sessile, mostly (2–) 3–5 times as long as broad, entire or toothed; mature pedicels usually spreading or ascending, mostly about twice as long as the bracts or shorter; calyx 2.5–4 (–5.5) mm long, about equaling or slightly exceeding the mature fruit; racemes all or mostly opposite.
8. Leaves (except rarely the lower) sessile, often ± clasping; stems and axis of inflorescence often glandular.
8. Leaves all distinctly petioled; stems and axis eglandular.
1. Flowers (and fruits) solitary in axils of ordinary leaves or in terminal spikes or racemes with bracts at base of pedicels (or flowers) usually equaling or surpassing the flowers and gradually reduced from the foliage leaves (leaves or bracts subtending flowers usually alternate); annual (except V. serpyllifolia and V. filiformis).
9. Flowers all in the axils of ordinary (but often alternate) foliage leaves, on pedicels (5–) 7–22 (–25) mm long and equaling or exceeding the subtending leaves; stems prostrate or widely spreading.
10. Leaves (at least the larger) palmately 3–5 lobed.
10. Leaves with ca. 7–15 rounded teeth.
11. Leaf blades reniform, broader than long, well-developed ones cordate at base; plant perennial, mat-forming with prostrate stems rooting at the nodes, not [or very rarely?] setting fruit; calyx lobes broadest beyond the middle, rounded at apex, with 1 vein.
11. Leaf blades mostly longer than broad, all truncate to tapered at the base; plant annual, ± prostrate but with taproot and not forming mats, setting fruit at maturity; calyx lobes broadest below the middle, ± acute, at maturity with 1–5 strong veins.
12. Capsule lobes divergent and usually angled at apex; corolla ca. 7.5–8.5 (–9.5) mm broad.
12. Capsule lobes not divergent (i.e., their axes nearly parallel) and broadly rounded at apex; corolla at most ca. 5–7 (–7.5) mm broad.
9. Flowers in the axils of bracts much smaller than the lower foliage leaves, on pedicels ca. 0.5–4.5 (–8) mm long and almost always shorter than the subtending bracts; stems (at least the flowering portion) erect or ascending from decumbent bases.
13. Blades of leaves and bracts glabrous or essentially so, mostly entire or obscurely crenulate (with minutely notched margins).
14. Flowers (and fruit) nearly sessile (pedicels ca. 0.5–1 mm long); stems glabrous or with gland-tipped hairs.
14. Flowers (at least the lower ones) on pedicels ca. 2–4.5 (–8) mm long at maturity; stem with minute ± upcurved pubescence (rarely glabrate or with spreading hairs—especially toward the inflorescence).
V. serpyllifolia (in part)
13. Blades of leaves and bracts clearly pubescent and/or ciliate, entire to toothed or lobed.
15. Leaves and bracts entire or merely crenate or toothed; style slightly shorter than the lobes of the capsule to slightly exceeding them.
15. Leaves (at least the upper) and often lower bracts ± deeply pinnately lobed toward the base; style various.
16. Style ca. 1–1.3 mm long, distinctly surpassing the capsule lobes; corolla ca. 4–5 mm broad; fruiting pedicels ca. 2–3.5 mm long.
16. Style ca. 0.5 mm long or less, shorter than the capsule lobes; corolla ca. 3 mm broad; fruiting pedicels ca. 1–2 (very rarely 2.5) mm long.