Flora of North America species comparison

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Ageratina thyrsiflora

Ageratina wrightii

congested snakeroot

Wright's snakeroot
Habit Perennials or subshrubs, 50–100 cm. Shrubs, 50–150 cm.
Stems

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

erect, puberulous.
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 proximally, alternate on distal 1/3–1/2 of stem;

petioles narrowly winged, 3–5(–8) mm;

blades ovate to deltate-ovate, mostly 1–2 × 0.5–1.5(–2) cm, bases truncate to cuneate or attenuate, margins entire or shallowly crenate, apices acute to blunt or obtuse, abaxial faces gland-dotted.
Peduncles

3–8 mm, puberulent.

1–3 mm, puberulent.
Involucres

2.5–3 mm.

3.5–4.5 mm.
Corollas

white (orange-veined), glabrous.

pinkish white to pink, glabrous.
Phyllaries

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

apices acute, abaxial faces puberulent.
Heads

clustered (in dense, terminal aggregates).

clustered.
Cypselae

hispid.

sparsely hispidulous.

Ageratina thyrsiflora

Ageratina wrightii
Phenology Flowering Sep–Nov. Flowering (Jul–)Aug–Oct(–Nov).
Habitat Rocky sites, oak woodland Limestone slopes, ledges, alluvium, in brushy vegetation
Elevation 1000–2200 m (3300–7200 ft) 1300–2200 m (4300–7200 ft)
Distribution
from FNA
AZ; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora)
[BONAP county map]
from FNA
AZ; NM; TX; Mexico
[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.)
Source FNA vol. 21, p. 553. FNA vol. 21, p. 552.
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. herbacea, A. jucunda, A. lemmonii, A. luciae-brauniae, A. occidentalis, A. paupercula, A. rothrockii, A. shastensis, A. thyrsiflora
Synonyms Kyrstenia thyrsiflora Eupatorium wrightii
Name authority (Greene) R. M. King & H. Robinson: Phytologia 19: 227. (1970) (A. Gray) R. M. King & H. Robinson: Phytologia 19: 228. (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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