Flora of North America species comparison

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Ageratina occidentalis

Ageratina thyrsiflora

western boneset, western eupatorium, western snakeroot

congested snakeroot
Habit Perennials or subshrubs, 15–70 cm (caudices woody, rhizomatous). Perennials or subshrubs, 50–100 cm.
Stems

(green or purple) erect or ascending, puberulent.

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

opposite proximally, alternate on distal 1/4–1/2 of stems;

petioles 5–12 mm;

blades triangular to ovate, 2.5–5 × 1.7–4 cm, bases truncate to cuneate, margins serrate, apices acute, abaxial faces gland-dotted.

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

2–5 mm, minutely puberulent.

3–8 mm, puberulent.
Involucres

3–3.5(–4) mm.

2.5–3 mm.
Corollas

pink, bluish, or white tinged with purple, lobes glabrous or glabrate.

white (orange-veined), glabrous.
Phyllaries

apices acute, abaxial faces viscid-puberulent and/or sessile-glandular.

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

clustered.

clustered (in dense, terminal aggregates).
Cypselae

sessile-glandular.

hispid.
2n

= 34.

Ageratina occidentalis

Ageratina thyrsiflora
Phenology Flowering (Jun–)Jul–Sep. Flowering Sep–Nov.
Habitat Crevices, outcrops, rocky slopes, ridges, talus, gravelly and sandy stream bars, mixed hardwood-conifer woodlands, aspen, open and brushy vegetation Rocky sites, oak woodland
Elevation (40–50)900–2800(–3200) m ((100–200)3000–9200(–10500) ft) 1000–2200 m (3300–7200 ft)
Distribution
from FNA
CA; ID; MT; NV; OR; UT; WA
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora)
[BONAP county map]
Discussion

Ageratina occidentalis is the only species of the genus in the flora area with sessile-glandular cypselae; peduncles also may be sessile-glandular. Its identity also can be confirmed among flora area species by its relatively long (5–6 mm) corollas.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

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. 552. FNA vol. 21, p. 553.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratina Asteraceae > tribe Eupatorieae > Ageratina
Sibling taxa
A. adenophora, A. altissima, A. aromatica, A. havanensis, A. herbacea, A. jucunda, A. lemmonii, A. luciae-brauniae, 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 occidentale Kyrstenia thyrsiflora
Name authority (Hooker) R. M. King & H. Robinson: Phytologia 19: 224. (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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