Flora of North America species comparison

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Ageratina adenophora

Ageratina shastensis

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

Mt. Shasta snakeroot, Shasta ageratina, Shasta snakeroot
Habit Subshrubs, 50–220 cm. Perennials, 15–45 cm (bases woody, enlarged, occasionally rhizomatous).
Stems

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

erect (clustered from bases), puberulent to pubescent (often with some glandular hairs distally).
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 proximally, alternate on at least distal 1/2 of stems;

petioles 4–6 mm;

blades (venation raised-reticulate) orbiculate (juvenile) or deltate-ovate, 1.5–3 × 1–2 cm, (subcoriaceous) bases obtuse to truncate, margins entire or coarsely serrate to dentate, apices acute to acuminate, abaxial faces ± gland-dotted and/or stipitate-glandular.
Peduncles

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

(0–)2–15 mm, puberulent and stipitate-glandular.
Involucres

3.5–4 mm.

10–11 mm.
Corollas

white, pink-tinged, lobes sparsely hispidulous.

white, glabrous.
Phyllaries

apices acute, abaxial faces stipitate-glandular.

apices acute, abaxial faces sparsely puberulent.
Heads

clustered.

mostly borne singly (each often subtended by a leaflike bract).
Cypselae

glabrous.

hispidulous.
2n

= 51.

= 34.

Ageratina adenophora

Ageratina shastensis
Phenology Flowering Mar–Aug(–Sep). Flowering Jun–Oct.
Habitat Stream margins, ditches, road embankments, hillsides Cracks and crevices of nearly vertical limestone cliffs
Elevation 400–900 m (1300–3000 ft) 400–1800 m (1300–5900 ft)
Distribution
from FNA
CA; Mexico; Intoduced [Also introduced in Europe, Pacific Islands (New Zealand)]
[WildflowerSearch map]
[BONAP county map]
from FNA
CA
[BONAP county map]
Discussion

Ageratina shastensis is recognized by relatively large solitary heads and coarsely serrate, subcoriaceous leaves alternate on distal parts of stems.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 553. FNA vol. 21, p. 552.
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. thyrsiflora, A. wrightii
Synonyms Eupatorium adenophorum Eupatorium shastense
Name authority (Sprengel) R. M. King & H. Robinson: Phytologia 19: 211. (1970) (D. W. Taylor & Stebbins) R. M. King & H. Robinson: Phytologia 45: 464. (1980)
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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