Perennials, (20-)40-70(-150) cm (slender, fibrous-rooted crowns, with slender rhizomes). Stems ascending to erect, puberulent to glabrate. Leaves opposite; petioles 2-20 mm; blades (3-5-nerved) lanceolate to lanceolate-ovate, mostly 3-6 × (1.5-)2-3 cm, bases obtuse to truncate, margins serrate to crenate, apices acute to acuminate, sparsely puberulent abaxially, mostly along nerves. Heads clustered. Peduncles 5-12(-20) mm, puberulent. Involucres 5-7 mm. Phyllaries: apices acute, abaxial faces glabrous or glabrescent, eglandular. Corollas white, lobes short-villous. Cypselae sparsely and finely strigose-hirsute. 2n = 85 [ca. 100, fide A. M. Powell on label].

Flowering (Jul-)Aug-Oct. Rocky slopes and ledges, in oak-juniper, pine-oak, pine, aspen, and spruce-fir woodland; 1700-2400 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua, Coahuila, Durango, Sonora).

Ageratina rothrockii is similar to A. altissima, probably its western vicariant, and the two perhaps would be justifiably treated as conspecific.

Duration: Perennial

Nativity: Native

Lifeform: Subshrub

General: Perennial herbs or subshrubs, to 70 cm tall or more, herbage puberulent to glabrate, plants arising from fibrous-rooted crowns with slender rhizomes.

Leaves: Leaves opposite, lanceolate to lance-ovate, to 6 cm long, with 3-5 nerves, margins serrate to crenulate, acute or acuminate at the tip, sparsely pubescent below.

Flowers: Heads discoid, disks white, with white, protruding stamens, corolla lobes short-villous, involucres 5-7 mm high, phyllaries with acute tips, the abaxial faces glabrous to glabrescent, borne on peduncles 5-12 mm.

Fruits: Achenes to 1 mm, sparsely and finely strigose-hirsute.

Ecology: Found on rocky slopes and ledges in pine-oak, oak-juniper, aspen, and spruce-fir, woodlands from 6,500-7,500 ft (1891-2286 m); flowering August-October.

Distribution: Arizona, New Mexico, Texas; Mexico.

Notes: Look for this species under Eupatorium rothrockii in older texts. The keys to this species are the short-villous corolla lobes, the involucre 5-7 mm high, and the lanceolate to lance-ovate leaves. Differentiate this species from A. herbacea by the larger involucre and the strongly hairy corolla lobes.

Ethnobotany: Unknown

Etymology: Ageratina is a dimunitive of Ageratum, which is from Greek ageratons for not growing old, while rothrockii is named for Dr. Joseph Trimble Rothrock (1839-1922), surgeon on the Wheeler expedition of 1873-1875.

Synonyms: Eupatorium rothrockii

Editor: LCrumbacher 2011