Flora of North America species comparison

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Ageratina adenophora

Ageratina thyrsiflora

Crofton weed, eupatory, Mexican devil, sticky snakeroot, thoroughwort

congested snakeroot
Habit Subshrubs, 50–220 cm. Perennials or subshrubs, 50–100 cm.
Stems

(usually purplish when young) erect, stipitate-glandular.

erect (usually forming compact ‘bushlets’), finely and evenly puberulent (hairs minute, bent).
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.

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.
Peduncles

5–12 mm, densely stipitate-glandular and sometimes also sparsely viscid-puberulent.

3–8 mm, puberulent.
Involucres

3.5–4 mm.

2.5–3 mm.
Corollas

white, pink-tinged, lobes sparsely hispidulous.

white (orange-veined), glabrous.
Phyllaries

apices acute, abaxial faces stipitate-glandular.

apices acute to obtuse (dark orange-veined), abaxial faces.
Heads

clustered.

clustered (in dense, terminal aggregates).
Cypselae

glabrous.

hispid.
2n

= 51.

Ageratina adenophora

Ageratina thyrsiflora
Phenology Flowering Mar–Aug(–Sep). Flowering Sep–Nov.
Habitat Stream margins, ditches, road embankments, hillsides Rocky sites, oak woodland
Elevation 400–900 m (1300–3000 ft) 1000–2200 m (3300–7200 ft)
Distribution
from FNA
CA; Mexico; Intoduced [Also introduced in Europe, Pacific Islands (New Zealand)]
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora)
[BONAP county map]
Discussion

Ageratina thyrsiflora is known from the United States from a single collection dated 1929 from “near Nogales” in Santa Cruz County. It is recognized by its strict, unbranched or few-branched stems with alternate, densely arranged leaves, relatively small heads densely clustered in terminal aggregates, orange-veined phyllaries and corollas, and closely puberulent stems and petioles (hairs minute, sharply upwardly bent).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 553. FNA vol. 21, p. 553.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratina Asteraceae > tribe Eupatorieae > Ageratina
Sibling taxa
A. altissima, A. aromatica, A. havanensis, A. herbacea, A. jucunda, A. lemmonii, A. luciae-brauniae, A. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. thyrsiflora, A. wrightii
A. adenophora, A. altissima, A. aromatica, A. havanensis, A. herbacea, A. jucunda, A. lemmonii, A. luciae-brauniae, A. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. wrightii
Synonyms Eupatorium adenophorum Kyrstenia thyrsiflora
Name authority (Sprengel) R. M. King & H. Robinson: Phytologia 19: 211. (1970) (Greene) R. M. King & H. Robinson: Phytologia 19: 227. (1970)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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