Flora of North America species comparison

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Ageratum conyzoides

Ageratum corymbosum

tropical whiteweed

flat-top whiteweed
Habit Annuals, perennials, or sub-shrubs, 20–150 cm (fibrous-rooted). Perennials or subshrubs, 30–100 cm (fibrous-rooted).
Stems

erect, sparsely to densely villous.

erect to basally decumbent, puberulent to minutely strigoso-hispid.
Leaf

blades ovate to elliptic-oblong, 2–8 × 1–5 cm, margins toothed, abaxial faces sparsely pilose and gland-dotted.

blades ovate to rhombic-lanceolate, 3–8 × 1–3.5 cm, margins toothed, abaxial faces usually puberulent, sometimes minutely strigoso-hispid, densely gland-dotted.
Peduncles

minutely puberulent and sparsely to densely pilose, eglandular.

finely puberulent (not pilose), eglandular.
Involucres

3–3.5 × 4–5 mm.

5–6 mm.
Corollas

usually blue to lavender, sometimes white.

usually blue to lavender, sometimes white.
Phyllaries

oblong-lanceolate (0.8–1.2 mm wide), glabrous or sparsely pilose (margins often ciliate), eglandular, tips abruptly tapering, subulate, 0.5–1 mm.

narrowly lanceolate (0.4–0.7 mm wide, innermost often 1–1.5 mm longer than outer), finely puberulent, eglandular, tips green or purplish, filiform.
Cypselae

sparsely strigoso-hispidulous;

pappi usually of scales 0.5–1.5(–3) mm, sometimes with tapering setae, rarely 0.

glabrous;

pappi usually crowns of connate scales with erose margins or tubular portions longer than divisions, rarely with 1 or more awnlike lobes.
2n

= 20, 40.

= 20, 30, 40.

Ageratum conyzoides

Ageratum corymbosum
Phenology Flowering Jul–Aug. Flowering Jul–Oct.
Habitat Disturbed sites, mostly coastal Crevices, ledges, cliffs, other rocky sites in canyons, along streams, in desert grasslands, oak-agave, oak, oak-juniper, and pine-oak woodlands
Elevation 0–20 m (0–100 ft) (900–)1200–1900 m ((3000–)3900–6200 ft)
Distribution
from FNA
AL; CA; CT; FL; GA; KY; MD; MO; MS; NC; HI; Central America; South America; West Indies [Introduced in North America; introduced, Mexico]
[BONAP county map]
from FNA
AZ; NM; Mexico
[WildflowerSearch map]
[BONAP county map]
Discussion

Ageratum conyzoides is apparently native to South America. North American plants were escapes and naturalized from cultivation.

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

Habitat information came mostly from collections from Sonora and Chihuahua, Mexico. Ageratum corymbosum grows in all Mexican states except for the extreme southeast. It has been included in various summaries as occurring in Texas; as noted by D. S. Correll and M. C. Johnston (1970), those records apparently were based on a collection by Charles Wright from southwestern New Mexico.

Varieties and forms of Ageratum corymbosum have been recognized (e.g., M. F. Johnson 1971; R. McVaugh 1984). McVaugh wryly noted that extremes of these intergrading infraspecific entities “can be recognized with a little imagination.” The form that reaches the United States (with ovate-lanceolate leaves) is var. jaliscense.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 21, p. 482. FNA vol. 21, p. 482.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. corymbosum, A. houstonianum, A. maritimum
A. conyzoides, A. houstonianum, A. maritimum
Synonyms A. latifolium A. corymbosum var. jaliscense, A. salicifolium, A. strictum
Name authority Linnaeus: Sp. Pl. 2: 839. (1753) Zuccagni: Cent. Observ. Bot., no. 85. (1806)
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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