Ageratina thyrsiflora (Greene) R.M. King & H. Rob.
Family: Asteraceae
Congested Snakeroot
Ageratina thyrsiflora image
National Museum of Natural History Image Collection  

Perennials or subshrubs, 50-100 cm. Stems erect (usually forming compact `bushlets´), finely and evenly puberulent (hairs minute, bent). Leaves usually alternate, sometimes subopposite (densely overlapping internodes); petioles 3-20 mm; blades ovate-lanceolate to triangular, 2.5-6.5 × 1-2.5(-3) cm, bases obtuse to cuneate, margins shallowly and coarsely crenate to serrate to subentire, apices rounded-obtuse, abaxial faces hirtellous. Heads clustered (in dense, terminal aggregates). Peduncles 3-8 mm, puberulent. Involucres 2.5-3 mm. Phyllaries: apices acute to obtuse (dark orange-veined), abaxial faces. Corollas white (orange-veined), glabrous. Cypselae hispid.

Flowering Sep-Nov. Rocky sites, oak woodland; 1000-2200 m; Ariz.; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora).

Ageratina thyrsiflora image
National Museum of Natural History Image Collection  
Ageratina thyrsiflora image
National Museum of Natural History Image Collection  
Ageratina thyrsiflora image
National Museum of Natural History Image Collection