Flora of North America species comparison

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Ageratum houstonianum

bluemink, floss flower, Houston's whiteweed
Habit Annuals, 30–80 cm (fibrous-rooted).
Stems

erect to decumbent, sparsely to densely pilose.
Leaf

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

viscid-puberulent, pilose, and stipitate-glandular.
Involucres

ca. 4 × 5–6 mm.
Corollas

usually lavender, rarely 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.
Cypselae

sparsely strigoso-hispidulous;

pappi of 5 distinct, oblong scales 2–3 mm.
2n

= 20.

Ageratum houstonianum
Phenology Flowering Jun–Aug.
Habitat Disturbed sites, mostly coastal
Elevation 0–20 m (0–100 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]
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.)
Source FNA vol. 21, p. 483.
Parent taxa Asteraceae > tribe Eupatorieae > Ageratum
Sibling taxa
A. conyzoides, A. corymbosum, A. maritimum
Synonyms A. conyzoides var. mexicanum
Name authority Miller: Gard. Dict. ed. 8, Ageratum no. 2. (1768)
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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