Flora of North America species comparison

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Ageratina aromatica

Ageratina thyrsiflora

lesser snakeroot, small-leaf white snakeroot

congested snakeroot
Habit Perennials, 30–80(–100) cm. Perennials or subshrubs, 50–100 cm.
Stems

erect, villous-puberulent.

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

opposite;

petioles 1–8(–12) mm;

blades narrowly to broadly deltate to nearly ovate or lanceolate, 2–7(–9) × 1.5–4 cm, (usually subcoriaceous) bases rounded or truncate to barely cuneate or subcordate, margins usually crenate, sometimes crenate-serrate to dentate or subentire, apices acute to obtuse, faces minutely pilose.

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.
Peduncles

2–9 mm, densely and closely puberulent.

3–8 mm, puberulent.
Involucres

3.5–5 mm.

2.5–3 mm.
Corollas

white, lobes sparsely villous.

white (orange-veined), glabrous.
Phyllaries

apices acute, abaxial faces puberulent to villous-puberulent.

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

clustered.

clustered (in dense, terminal aggregates).
Cypselae

usually glabrous or sparsely puberulent (near apices), rarely hirtellous on angles.

hispid.
2n

= 34.

Ageratina aromatica

Ageratina thyrsiflora
Phenology Flowering late Aug–Oct(–Nov). Flowering Sep–Nov.
Habitat Sandy soils, burned pinelands, turkey oak sand ridges, pine-oak and oak-hickory upland woods, old fields, roadsides, fencerows, moist sites Rocky sites, oak woodland
Elevation 100–900 m (300–3000 ft) 1000–2200 m (3300–7200 ft)
Distribution
from FNA
AL; CT; DE; FL; KY; LA; MA; MD; MS; NC; NJ; NY; OH; PA; RI; SC; TN; VA; WV
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; Mexico (Chihuahua, Durango, Jalisco, Sinaloa, Sonora)
[BONAP county map]
Discussion

Intergrades (probable hybrids) between Ageratina aromatica and A. altissima were identified by A. F. Clewell and J. W. Wooten (1971) over a broad area of their sympatry. They also found intergrades between A. aromatica and A. jucunda where their ranges meet.

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

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. 550. FNA vol. 21, p. 553.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratina Asteraceae > tribe Eupatorieae > Ageratina
Sibling taxa
A. adenophora, A. altissima, 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. shastensis, A. wrightii
Synonyms Eupatorium aromaticum, Eupatorium latidens Kyrstenia thyrsiflora
Name authority (Linnaeus) Spach: Hist. Nat. Vég. 10: 286. (1841) (Greene) R. M. King & H. Robinson: Phytologia 19: 227. (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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