Ageratum conyzoides

Linnaeus

Sp. Pl. 2: 839. 1753

Common names: Tropical whiteweed
Synonyms: Ageratum latifolium Cavanilles
Treatment appears in FNA Volume 21. Treatment on page 482. Mentioned on page 483.
Annuals, perennials, or sub-shrubs, 20–150 cm (fibrous-rooted). Stems erect, sparsely to densely villous. Leaf blades ovate to elliptic-oblong, 2–8 × 1–5 cm, margins toothed, abaxial faces sparsely pilose and gland-dotted. Peduncles minutely puberulent and sparsely to densely pilose, eglandular. Involucres 3–3.5 × 4–5 mm. Phyllaries oblong-lanceolate (0.8–1.2 mm wide), glabrous or sparsely pilose (margins often ciliate), eglandular, tips abruptly tapering, subulate, 0.5–1 mm. Corollas usually blue to lavender, sometimes white. Cypselae sparsely strigoso-hispidulous; pappi usually of scales 0.5–1.5(–3) mm, sometimes with tapering setae, rarely 0. 2n = 20, 40.

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

Distribution

V21-1212-distribution-map.gif

Ala., Calif., Conn., Fla., Ga., Ky., Md., Miss., Mo., N.C., South America, introduced, Mexico, West Indies, Central America, Pacific Islands (Hawaii).

Discussion

Ageratum conyzoides is apparently native to South America. North American plants were escapes and naturalized from cultivation.

References

None.

Lower Taxa

No lower taxa listed.