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.
Duration: Perennial
Nativity: Native
Lifeform: Subshrub
General: Perennial herbs or subshrubs to 80 cm tall, sometimes from a woody crown or woody rhizomes; stems erect, puberulent, often brittle.
Leaves: Opposite and petiolate, the petioles 1-2.5 cm; blades triangular to broadly ovate, to 8 cm long, truncate to subcordate at the base, acute or acuminate at the tip, the margins toothed, the upper surface sparsely hispidulous to glabrate; color is often yellow-green but can be grayish.
Flowers: Flower heads discoid, in dense or open clusters, on peduncles to 1.5 cm; involucre (the ring of bracts surrounding each flower head) campanulate, 3-4 mm high, the bracts in 2 series, subequal, lanceolate with acuminate tips, puberulent; flowers are all discs (radial, bisexual, with a 5-lobed corolla), 10-20 per head, with white corollas and protruding stamens.
Fruits: Achenes to 2 mm long, finely strigose-hispidulous.
Ecology: Found in rocky areas along streams, slopes, ridges, and washes, in open pine forests and juniper woodlands, from 5,000-9,000 ft (1524-2743 m); flowers August-October.
Distribution: CA and NV east to CO, NM, and TX; south to n MEX.
Notes: Look for this species under Eupatorium herbaceum in the older texts. The keys to this species are the opposite, petiolate leaves, often yellow-green in color; the glabrous corolla lobes; the involucres 3-4 mm high with 2 rows of subequal phyllaries (bracts); and the woody root crowns. This species looks like a Brickellia except for its toothed and deeply veined leaves.
Ethnobotany: A cold infusion or lotion was used for headache, cold, or fever.
Etymology: Ageratina is a dimunitive of Ageratum, which is from Greek ageratons for not growing old, while herbacea means herbaceous.
Synonyms: Eupatorium herbaceum
Editor: LCrumbacher 2011, FSCoburn 2015, AHazelton 2015
