Plants annual. Stems reddish or ± purple-red spotted, branched apically, densely retrorse white pubescent, nodes glabrous or villous. Petiole 2-15 mm; leaf blade lanceolate-ovate to ovate, ca. 8 cm × 3 mm, base rounded to subtruncate, margin unequally serrate, apex acuminate. Verticillasters in terminal capitula to 5 cm in diam.; floral leaves leaflike, reduced, densely pubescent, glandular, short petiolate or subsessile, margin entire; bracteoles linear, ca. 1 cm, curved upward, pilose, glandular. Pedicel ca. 1 mm, puberulent. Calyx tubular, narrow, 7-9 mm, pubescent, brown glandular outside, white bearded at throat inside; teeth subulate, equal, ca. 1 mm, apex spinescent. Corolla purple-red, 3-4 × as long as calyx, densely pubescent, glandular; upper lip slightly recurved inward, entire; lower lip ± patent. Nutlets obovoid, truncate. Fl. Jun-Jul.
"Pleasantly aromatic rhizomatous perennial 5–12 dm, often branched; stems usually hairy at least above; lvs deltoid-lanceolate to lanceolate or rarely ovate, acuminate, ± serrate, rounded or truncate to broadly acute at base, thinly hairy or glabrous to conspicuously hairy above or canescent beneath, the larger 6–10 cm on petioles 1–1.5 cm; heads 1–3.5 cm wide (excluding the cors); bracteal lvs lanceolate or ovate; cal 7–10 mm, puberulent, its throat densely hirsute internally with erect white hairs a third to half as long as the cal-lobes, these subulate, 1–2 mm; cor bright (but rather pale) lavender, 2–3.5 cm, the somewhat arcuate upper lip densely villous at the tip; 2n=32, 34, 36. Upland woods, thickets, and prairies. Que. to Man. and B.C., s. to Ga., La., and Ariz. June–Sept. (M. mollis, the common form with the hairs of the stem decurved) Most of our plants are var. fistulosa, as principally described above. The western var. menthaefolia (Graham) Fernald, a shorter, less branched plant, often with a single head, the longest petioles seldom over 1 cm, enters our range in w. Minn. (M. menthaefolia)"