Flora of North America species comparison

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Ageratum houstonianum

Ageratum corymbosum

bluemink, floss flower, Houston's whiteweed

flat-top whiteweed
Habit Annuals, 30–80 cm (fibrous-rooted). Perennials or subshrubs, 30–100 cm (fibrous-rooted).
Stems

erect to decumbent, sparsely to densely pilose.

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

blades deltate to ovate, mostly 3–8 × 2.5–4 cm, margins toothed, abaxial faces sparsely to densely pilose, not evidently 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

viscid-puberulent, pilose, and stipitate-glandular.

finely puberulent (not pilose), eglandular.
Involucres

ca. 4 × 5–6 mm.

5–6 mm.
Corollas

usually lavender, rarely white.

usually blue to lavender, sometimes white.
Phyllaries

narrowly lanceolate (0.6–1 mm wide), stipitate-glandular, sparsely to densely pilose, eciliate or inconspicuously ciliate, tips gradually tapering, indurate-subulate, 0.8–2 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 of 5 distinct, oblong scales 2–3 mm.

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.

= 20, 30, 40.

Ageratum houstonianum

Ageratum corymbosum
Phenology Flowering Jun–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; CT; FL; GA; MA; NC; SC; TX; Mexico; Central America [Introduced in North America; introduced, Pacific Islands (Hawaii)]
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; NM; Mexico
[WildflowerSearch map]
[BONAP county map]
Discussion

Ageratum houstonianum is apparently native to southeastern Mexico and Central America; the North American plants are escapes and naturalized from cultivars. M. F. Johnson (1971) observed that forma isochroum (B. L. Robinson) M. F. Johnson (type from the state of Veracruz, Mexico) sometimes may be nearly eglandular.

(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. 483. FNA vol. 21, p. 482.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. conyzoides, A. corymbosum, A. maritimum
A. conyzoides, A. houstonianum, A. maritimum
Synonyms A. conyzoides var. mexicanum A. corymbosum var. jaliscense, A. salicifolium, A. strictum
Name authority Miller: Gard. Dict. ed. 8, Ageratum no. 2. (1768) 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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