Flora of North America species comparison

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Ageratum corymbosum

flat-top whiteweed
Habit Perennials or subshrubs, 30–100 cm (fibrous-rooted).
Stems

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

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

finely puberulent (not pilose), eglandular.
Involucres

5–6 mm.
Corollas

usually blue to lavender, sometimes white.
Phyllaries

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

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, 30, 40.

Ageratum corymbosum
Phenology Flowering Jul–Oct.
Habitat Crevices, ledges, cliffs, other rocky sites in canyons, along streams, in desert grasslands, oak-agave, oak, oak-juniper, and pine-oak woodlands
Elevation (900–)1200–1900 m ((3000–)3900–6200 ft)
Distribution
from FNA
AZ; NM; Mexico
[WildflowerSearch map]
[BONAP county map]
Discussion

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.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. conyzoides, A. houstonianum, A. maritimum
Synonyms A. corymbosum var. jaliscense, A. salicifolium, A. strictum
Name authority 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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