Ageratum corymbosum

Zuccagni

Cent. Observ. Bot., no. 85. 1806

Common names: Flat-top whiteweed
Illustrated
Synonyms: Ageratum corymbosum var. jaliscense B. L. Robinson Ageratum salicifolium Hemsley Ageratum strictum
Treatment appears in FNA Volume 21. Treatment on page 482. Mentioned on page 481.

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. 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. Corollas usually blue to lavender, sometimes white. 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.


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

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.

Selected References

None.

Lower Taxa

None.

... more about "Ageratum corymbosum"
Guy L. Nesom +
Zuccagni +
Flat-top whiteweed +
Ariz. +, N.Mex. +  and Mexico. +
(900–)1200–1900 m +
Crevices, ledges, cliffs, other rocky sites in canyons, along streams, in desert grasslands, oak-agave, oak, oak-juniper, and pine-oak woodlands +
Flowering Jul–Oct. +
Cent. Observ. Bot., no. +
Illustrated +
Ageratum corymbosum var. jaliscense +, Ageratum salicifolium +  and Ageratum strictum +
Ageratum corymbosum +
Ageratum +
species +