Plants annual, robust; taproot slender. Stems erect, branched distally, usually reddish, (20-)50-100 cm, coarsely hispid. Leaves 2 per node; proximal petiolate, blade lanceolate-spatulate, 3-10 cm × 6-30 mm (including petiole), base tapering into petiole as long as lamina; cauline sessile or nearly so, smaller distally, blade lanceolate-cuneate, 1.5-5 cm × 3-15 mm, apex acute, hispid on both surfaces. Inflorescences with many ascending, elongate branches, many-flowered, open, setose, glandular or not but not viscid; flowers 1 per node; bracts ranging from resembling leaves to narrowly lanceolate, 5-10 mm, apex caudate-acuminate. Flowers subsessile; calyx prominently 10-veined, not inflated, setose, lobed, tubular in flower, ovoid and (7-)10-15 × 2.5-4 mm in fruit, veins parallel, with pale commissures; lobes 5, spreading to recurved, narrowly lanceolate, 2-3 mm, apex acuminate; petals white, rarely pink, clawed, claw equaling calyx, limb obovate but deeply 2-lobed, 5-9 mm, apex truncate, appendages 0.2 mm; stamens exceeding petals, reduced to staminodes in some flowers; filaments white; styles 3, white, ca. 2 times calyx. Capsules enclosed in calyx, ellipsoid, opening by 6 spreading, lanceolate teeth; carpophore stout, 1.5-4 mm, glabrous. Seeds grayish brown to black, broadly reniform with concave faces, ca. 1 mm diam., rugose. 2n = 24.

Flowering summer. Cultivated land, roadsides, burnt clearings in forests, disturbed prairies; 0-2200 m; introduced; B.C., Nfld. and Labr. (Nfld.), Ont., Que., Sask.; Calif., Colo., Conn., Ga., Idaho, Ill., Ind., Iowa, Ky., Maine, Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Y., N.C., Ohio, Oreg., Pa., Tenn., Tex., Vt., Va., Wash., W.Va., Wis., Wyo.; Europe.

Subspecies dichotoma is an occasional adventive weed.