Flora of North America species comparison

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Ageratina adenophora

Ageratina rothrockii

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

Rothrock's snakeroot
Habit Subshrubs, 50–220 cm. Perennials, (20–)40–70(–150) cm (slender, fibrous-rooted crowns, with slender rhizomes).
Stems

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

ascending to erect, puberulent to glabrate.
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.

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

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

5–12(–20) mm, puberulent.
Involucres

3.5–4 mm.

5–7 mm.
Corollas

white, pink-tinged, lobes sparsely hispidulous.

white, lobes short-villous.
Phyllaries

apices acute, abaxial faces stipitate-glandular.

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

clustered.

clustered.
Cypselae

glabrous.

sparsely and finely strigose-hirsute.
Powell

on label].
2n

= 51.

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

Ageratina adenophora

Ageratina rothrockii
Phenology Flowering Mar–Aug(–Sep). Flowering (Jul–)Aug–Oct.
Habitat Stream margins, ditches, road embankments, hillsides Rocky slopes and ledges, in oak-juniper, pine-oak, pine, aspen, and spruce-fir woodland
Elevation 400–900 m (1300–3000 ft) 1700–2400 m (5600–7900 ft)
Distribution
from FNA
CA; Mexico; Intoduced [Also introduced in Europe, Pacific Islands (New Zealand)]
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; NM; TX; Mexico (Chihuahua, Coahuila, Durango, Sonora)
[WildflowerSearch map]
[BONAP county map]
Discussion

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. 553. FNA vol. 21, p. 550.
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. shastensis, A. thyrsiflora, A. wrightii
Synonyms Eupatorium adenophorum Eupatorium rothrockii
Name authority (Sprengel) R. M. King & H. Robinson: Phytologia 19: 211. (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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