Sp. Pl. 1: 10. 1753
Perennials. Stems erect, usually with 10–20 nodes, (50–)70–120(–150) cm, proximal 1/2 glabrous, distal 1/2 eglandular-hairy with some glandular hairs intermixed. Leaves: blade narrowly ovate-lanceolate, almost linear, or narrowly ovate, (60–)80–120(–150) × 10–30(–35) mm, base cuneate, truncate, or cordate, margins serrate to biserrate, apex acute, surfaces sparsely or densely eglandular-hairy, rarely glabrous. Racemes 1–7(–9), terminal and occasionally axillary, 100–200(–300) mm, 150–300-flowered, axis eglandular- and glandular-hairy; bracts linear to subulate, 2–6 mm. Pedicels erect, (1–)1.5–3(–5) mm, shorter than subtending bract, densely eglandular-hairy, sometimes also glandular-hairy. Flowers: calyx lobes 2–2.5(–4) mm, apex acute, eglandular-hairy, sometimes glandular-hairy; corolla blue, campanulate, longer than wide, 5–7 mm diam.; stamens 5–6 mm; style (5–)6–8(–10) mm. Capsules ± compressed in cross section, ovoid, 2.5–3 × 2.5–3 mm, apex emarginate, glabrous. Seeds 2–40, light brown, ellipsoid, flat, 0.7–1.2 × 0.5–0.8 mm, 0.2–0.3 mm thick, smooth. 2n = 34, 68 (Eurasia).
Phenology: Flowering Jun–Aug(–Sep).
Habitat: Moist (swampy) habitats, roadsides.
Elevation: 0–800 m.
Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon, Alaska, Conn., Fla., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., N.Dak., Ohio, Pa., R.I., Vt., Wash., W.Va., Wis., Eurasia, introduced also in South America, Pacific Islands (New Zealand).
Reports of Veronica bachofenii Heuffel, V. grandis Fischer ex Sprengel (= V. daurica Steven), or V. spuria Linnaeus, seem always to refer to garden varieties of V. longifolia. Garden varieties often differ from typical plants in having glandular hairs and broader leaves, which may indicate past hybridization with other species.
Subgenus Pseudolysimachium includes Veronica longifolia and V. spicata, which are naturalized in the flora area, but also other species and hybrids of these, which are commonly grown ornamentally and may escape from cultivation. All of these plants should easily key out with V. longifolia and V. spicata but differ in specifics of the species descriptions.