Ageratum houstonianum

Miller

Gard. Dict. ed. 8, Ageratum no. 2. 1768

Common names: Bluemink
Synonyms: Ageratum conyzoides var. mexicanum (Sims) de Candolle
Treatment appears in FNA Volume 21. Treatment on page 483. Mentioned on page 482.
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. 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. Corollas usually lavender, rarely white. Cypselae sparsely strigoso-hispidulous; pappi of 5 distinct, oblong scales 2–3 mm. 2n = 20.

Phenology: Flowering Jun–Aug.
Habitat: Disturbed sites, mostly coastal
Elevation: 0–20 m

Distribution

V21-1213-distribution-map.gif

Ala., Conn., Fla., Ga., Mass., N.C., S.C., Tex., Mexico, Central America, introduced, Pacific Islands (Hawaii).

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.

References

None.

Lower Taxa

No lower taxa listed.