Flora of North America species comparison

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Ageratina occidentalis

Ageratina rothrockii

western boneset, western eupatorium, western snakeroot

Rothrock's snakeroot
Habit Perennials or subshrubs, 15–70 cm (caudices woody, rhizomatous). Perennials, (20–)40–70(–150) cm (slender, fibrous-rooted crowns, with slender rhizomes).
Stems

(green or purple) erect or ascending, puberulent.

ascending to erect, puberulent to glabrate.
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.

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.
Peduncles

2–5 mm, minutely puberulent.

5–12(–20) mm, puberulent.
Involucres

3–3.5(–4) mm.

5–7 mm.
Corollas

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

white, lobes short-villous.
Phyllaries

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

apices acute, abaxial faces glabrous or glabrescent, eglandular.
Heads

clustered.

clustered.
Cypselae

sessile-glandular.

sparsely and finely strigose-hirsute.
Powell

on label].
2n

= 34.

= 85 [ca. 100, fide A. M.

Ageratina occidentalis

Ageratina rothrockii
Phenology Flowering (Jun–)Jul–Sep. Flowering (Jul–)Aug–Oct.
Habitat Crevices, outcrops, rocky slopes, ridges, talus, gravelly and sandy stream bars, mixed hardwood-conifer woodlands, aspen, open and brushy vegetation Rocky slopes and ledges, in oak-juniper, pine-oak, pine, aspen, and spruce-fir woodland
Elevation (40–50)900–2800(–3200) m ((100–200)3000–9200(–10500) ft) 1700–2400 m (5600–7900 ft)
Distribution
from FNA
CA; ID; MT; NV; OR; UT; WA
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; NM; TX; Mexico (Chihuahua, Coahuila, Durango, Sonora)
[WildflowerSearch map]
[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 rothrockii is similar to A. altissima, probably its western vicariant, and the two perhaps would be justifiably treated as conspecific.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 552. FNA vol. 21, p. 550.
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. shastensis, A. thyrsiflora, A. wrightii
Synonyms Eupatorium occidentale Eupatorium rothrockii
Name authority (Hooker) R. M. King & H. Robinson: Phytologia 19: 224. (1970) (A. Gray) R. M. King & H. Robinson: Phytologia 19: 216. (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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