3. Pycnanthemum pilosum Nutt. (hairy mountain mint)

P. verticillatum (Michx.) Pers. var. pilosum (Nutt.) Cooperr.

Pl. 440 c, d; Map 1984

Stems 50–150 cm long, moderately to densely pubescent on the angles and sides with mostly short, spreading hairs. Leaves sessile or very short-petiolate, the largest leaves with the petioles 1–3 mm long. Leaf blades 2–8 cm long, 4–20 mm wide (those of the largest leaves 8–20 mm), lanceolate, elliptic-lanceolate, elliptic, or oblong-elliptic, mostly narrowly angled or tapered at the base, the margins usually entire, less commonly with a few shallow teeth, the upper surface glabrous or sparsely short-hairy, green, the undersurface grayish green, moderately to densely pubescent with relatively long, spreading hairs. Inflorescences relatively dense, often appearing broadly rounded, only the lowermost branches observable. Bracts similar to the foliage leaves, not whitened, but usually grayish green, densely pubescent with short, curled hairs on the upper surface, moderately to densely pubescent with relatively long, spreading hairs on the undersurface. Bractlets 3–5 mm long, linear to narrowly lanceolate. Calyces 3.5–4.5 mm long, actinomorphic or nearly so, densely pubescent with relatively long, woolly hairs, lacking longer bristly hairs on the margins or tip, the lobes all similar in size and shape 0.5–1.0 mm long, triangular, sharply pointed and usually with a minute, bristly extension of the midnerve. Corollas 5–8 mm long, white to pale lavender. Nutlets 1.0–1.3 mm long, sparsely hairy toward the tip. 2n=ca. 76–78. July–September.

Scattered nearly throughout the state (eastern U.S. west to Nebraska and Texas; Canada). Mesic to dry upland forests, upland prairies, savannas, glades, ledges and tops of bluffs, banks of streams and rivers, margins of lakes, and occasionally bottomland forests; also old fields, cemeteries, railroads, roadsides, and open, disturbed areas.

Where this species grows in proximity to P. albescens, rare putative hybrids have been collected. Steyermark (1963) noted that hairy mountain mint is a favorite bee plant.

This species is very closely related to P. verticillatum of the eastern United States. Some authors have treated the two as varieties of that species (Gleason and Cronquist, 1991). According to E. Grant and Epling (1943), true P. verticillatum differs from P. pilosum in its stems that are hairy only on the angles and in its densely hairy bracts. The leaves of P. verticillatum also tend to be more sparsely hairy on the undersurface with the hairs confined mostly to the veins.