Description: Annual herbs or perennial shrubs.
Leaves usually opposite, the upper sometimes alternate, margins toothed, petiolate.
Inflorescence terminal corymbs, heads clustered, many-flowered; heads short-cylindrical to campanulate; involucral bracts numerous, ± herbaceous, imbricate, ± equal, 2- or 3-seriate, shorter than the florets; receptacle naked conical. Ray florets absent. Disc florets bisexual, tubular, 5-toothed. Anthers obtuse at the base, with apical appendage. Style branches elongate, exserted.
Achenes narrowed at the base, 5-angled, ribbed; pappus of 5–10 short scales, free or united at the base, or reduced to annular crown or obsolete.
Distribution and occurrence: World: c. 60 species, Central & South America. Australia: 2 species (naturalized), Qld, N.S.W., N.T.
Text by M. F. Porteners
Taxon concept:
| | Key to the species | |
| 1 | Involucral bracts glabrous, oblong, non-glandular, apex short-acuminate to acute, margin erose to fimbriate, rarely entire; heads 3–6 mm diam.; leaves ovate, obtuse at base | Ageratum conyzoides |
| Involucral bracts hairy, linear-lanceolate, glandular, apex long-acuminate, margin entire; heads mostly 6–8 mm diam.; leaves ovate to triangular, cordate to truncate at base | Ageratum houstonianum |
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