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

white snakeroot

Habit Subshrubs, 50–220 cm. Perennials, (30–)50–80(–120) cm (bases usually fibrous-rooted crowns, sometimes rhizomatous).
Stems

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

ascending to erect, sometimes semiscandent, puberulent (hairs minute, crisped).

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 (5–)10–30(–50) mm;

blades usually deltate-ovate to ovate or broadly lanceolate, sometimes ovate-lanceolate, 4–11(–13) × 2.5–8(–9) cm, bases usually rounded to truncate or obtuse, sometimes cordate, margins coarsely and doubly incised-serrate, apices usually acuminate.

Peduncles

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

1–5 mm, puberulent.

Involucres

3.5–4 mm.

4–5 mm.

Corollas

white, pink-tinged, lobes sparsely hispidulous.

white, lobes sparsely short-villous.

Phyllaries

apices acute, abaxial faces stipitate-glandular.

apices acute, abaxial faces glabrous or sparsely and finely villous.

Heads

clustered.

clustered.

Cypselae

glabrous.

glabrous.

2n

= 51.

Ageratina adenophora

Ageratina altissima

Phenology Flowering Mar–Aug(–Sep).
Habitat Stream margins, ditches, road embankments, hillsides
Elevation 400–900 m (1300–3000 ft)
Distribution
from FNA
CA; Mexico; Intoduced [Also introduced in Europe, Pacific Islands (New Zealand)]
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; CT; DE; FL; GA; IA; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; NC; ND; NE; NH; NJ; NY; OH; OK; PA; RI; SC; SD; TN; TX; VA; VT; WI; WV; NB; NS; ON; QC; SK
[WildflowerSearch map]
[BONAP county map]
Discussion

Varieties 2 (2 in the flora).

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

Key
1. Phyllaries 3–5 mm, apices not cuspidate
var. altissima
1. Phyllaries 4–7 mm, apices cuspidate to acuminate
var. roanensis
Source FNA vol. 21, p. 553. FNA vol. 21, p. 549.
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. aromatica, A. havanensis, A. herbacea, A. jucunda, A. lemmonii, A. luciae-brauniae, A. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. thyrsiflora, A. wrightii
Subordinate taxa
A. altissima var. altissima, A. altissima var. roanensis
Synonyms Eupatorium adenophorum Ageratum altissimum
Name authority (Sprengel) R. M. King & H. Robinson: Phytologia 19: 211. (1970) (Linnaeus) R. M. King & H. Robinson: Phytologia 19: 212. (1970)
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