Flora of North America species comparison

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Ageratina thyrsiflora

Ageratina herbacea

congested snakeroot

desert ageratina, fragrant snakeroot, white thoroughwort
Habit Perennials or subshrubs, 50–100 cm. Perennials or subshrubs, (20–)30–60(–80) cm (woody crowns and woody rhizomes).
Stems

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

erect (brittle), minutely puberulent.
Leaves

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.

opposite;

petioles 10–25 mm;

blades triangular to lanceolate-ovate or ovate, 2–5(–7) × 1.5–3.5(–4.5) cm, bases truncate to shallowly cordate, margins dentate to serrate-dentate, abaxial faces sparsely hispidulous to glabrate, eglandular.
Peduncles

3–8 mm, puberulent.

4–15 mm, puberulent.
Involucres

2.5–3 mm.

4–5 mm.
Corollas

white (orange-veined), glabrous.

white, glabrous.
Phyllaries

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

apices acute, abaxial faces granular-puberulent.
Heads

clustered (in dense, terminal aggregates).

clustered.
Cypselae

hispid.

finely strigose-hispidulous.
2n

= 34.

Ageratina thyrsiflora

Ageratina herbacea
Phenology Flowering Sep–Nov. Flowering (Jul–)Aug–Oct.
Habitat Rocky sites, oak woodland Pine, pine-oak, juniper, and pinyon-juniper woodlands, rocks along streams, slopes, ridges, washes
Elevation 1000–2200 m (3300–7200 ft) 1400–2700(–2900) m (4600–8900(–9500) ft)
Distribution
from FNA
AZ; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora)
[BONAP county map]
from FNA
AZ; CA; CO; NM; NV; TX; UT; Mexico (Baja California, Chihuahua, Coahuila, Sonora)
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)

Ageratina herbacea is recognized by the distinctive color of its usually yellow-green, sometimes grayish, leaves, granular-puberulent involucres (with minute, thickened, eglandular hairs), and woody rhizomes.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 553. FNA vol. 21, p. 551.
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. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. wrightii
A. adenophora, A. altissima, A. aromatica, A. havanensis, A. jucunda, A. lemmonii, A. luciae-brauniae, A. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. thyrsiflora, A. wrightii
Synonyms Kyrstenia thyrsiflora Eupatorium ageratifolium var. herbaceum, Eupatorium herbaceum
Name authority (Greene) R. M. King & H. Robinson: Phytologia 19: 227. (1970) (A. Gray) R. M. King & H. Robinson: Phytologia 19: 222. (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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