Ageratina adenophora

Subshrubs, 50-220 cm. Stems (usually purplish when young) erect, stipitate-glandular. Leaves opposite; petioles 10-25 mm; blades (abaxially purple) ovate-lanceolate or ovate-deltate to lanceolate-ovate, (1.5-)2.5-5.5(-8) × 1.5-4(-6) cm, bases cuneate to obtuse or nearly truncate, margins serrate, apices acute to acuminate, abaxial faces stipitate- to sessile-glandular. Heads clustered. Peduncles 5-12 mm, densely stipitate-glandular and sometimes also sparsely viscid-puberulent. Involucres 3.5-4 mm. Phyllaries: apices acute, abaxial faces stipitate-glandular. Corollas white, pink-tinged, lobes sparsely hispidulous. Cypselae glabrous. 2n = 51.

Flowering Mar-Aug(-Sep). Stream margins, ditches, road embankments, hillsides; 400-900 m; intoduced; Calif.; Mexico; also introduced in Europe, Pacific Islands (New Zealand).