Perennials or subshrubs, (20-)30-60(-80) cm (woody crowns and woody rhizomes). Stems erect (brittle), minutely puberulent. Leaves opposite; petioles 10-25 mm; blades triangular to lanceolate-ovate or ovate, 2-5(-7) × 1.5-3.5(-4.5) cm, bases truncate to shallowly cordate, margins dentate to serrate-dentate, abaxial faces sparsely hispidulous to glabrate, eglandular. Heads clustered. Peduncles 4-15 mm, puberulent. Involucres 4-5 mm. Phyllaries: apices acute, abaxial faces granular-puberulent. Corollas white, glabrous. Cypselae finely strigose-hispidulous. 2n = 34. Flowering (Jul-)Aug-Oct. Pine, pine-oak, juniper, and pinyon-juniper woodlands, rocks along streams, slopes, ridges, washes; 1400-2700(-2900) m; Ariz., Calif., Colo., Nev., N.Mex., Tex., Utah; Mexico (Baja California, Chihuahua, Coahuila, Sonora). Ageratina herbacea is recognized by the distinctive color of its usually yellow-green, sometimes grayish, leaves, granular-puberulent involucres (with minute, thickened, eglandular hairs), and woody rhizomes.

Plant: Perennial shrubs; caudex woody; stem 4.5-7 dm, erect or spreading, green, puberulent Leaves: generally opposite; blade generally triangular to ± cordate, yellowish to light or grayish green, glabrous to puberulent INFLORESCENCE: heads, each resembling a flower; 6-8 mm, in dense clusters; phyllaries puberulent, subequal, in 1-2(3) series; receptacle flat to conic, naked Flowers: 10-60; corollas white, cylindric (or throat wider) Fruit: 2-3 mm achenes, 5-angled, generally 5-ribbed; pappus of 5-40 slender scabrous bristles, often easily detached Misc: Rocky pinyon/juniper woodland; 1600-2200 m.; May-Jun, Oct-Nov