Sp. Pl. 1: 13. 1753.
Annuals. Stems erect to ascending, 1–30(–40) cm, glandular- or eglandular-hairy. Leaves in 3–6 pairs per stem; blade oblong to broadly ovate, (2–)5–14(–35) × (2–)3–10(–18) mm, 2.5 times as long as wide, base truncate, margins crenate-serrate, apex obtuse to rounded, surfaces sparsely eglandular-hairy, rarely also glandular-hairy. Racemes 1(–3), terminal, 20–150 mm, (5–)15–40(–60)-flowered, axis densely eglandular- and glandular-hairy; bracts linear-oblong, (3.5–)4–6(–10) mm. Pedicels erect, 0–4 mm, shorter than subtending bract, densely eglandular- and glandular-hairy. Flowers: calyx lobes (2–)3.5–5(–6) mm, 0.8–2 mm wide, apex acute, glandular-hairy; corolla sky blue to intense blue, 2–4 mm diam.; stamens 0.3–0.5 mm; style (0.2–)0.4–0.6(–1) mm. Capsules compressed in cross section, obcordiform, 2–4 × 2.5–5 mm, apex markedly emarginate, glandular-ciliate, otherwise glabrous. Seeds 10–30, yellowish, ovoid, flat, 0.7–1.7 × 0.4–1 mm, 0.2–0.4 mm thick, rugose. 2n = 16.
Phenology: Flowering (Feb–)Mar–Jun(–Oct).
Habitat: Disturbed sites, lawns, fields, open forests, scrub, grasslands, rocky sites, coasts.
Elevation: 0–2900 m.
Introduced; Greenland, B.C., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que., Yukon, Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Eurasia, Africa, Atlantic Islands, Pacific Islands, Australia, introduced also in Mexico, Central America.